diff --git a/Elsa.sln b/Elsa.sln
index 9e4b96eda..d5b8e012b 100644
--- a/Elsa.sln
+++ b/Elsa.sln
@@ -514,8 +514,11 @@ EndProject
 Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Elsa.UserTasks.Persistence.EFCore.UnitTests", "test\unit\Elsa.UserTasks.Persistence.EFCore.UnitTests\Elsa.UserTasks.Persistence.EFCore.UnitTests.csproj", "{A4F3CB08-759D-4FE6-B715-E8D91E3E3F3E}"
 EndProject
 Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Elsa.UserTasks.Persistence.ConformanceTests", "test\unit\Elsa.UserTasks.Persistence.ConformanceTests\Elsa.UserTasks.Persistence.ConformanceTests.csproj", "{0C16ED4D-2483-488D-9CA1-D269ED5BEB9F}"
+EndProject
 Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Elsa.Hosts.SmokeTests", "test\integration\Elsa.Hosts.SmokeTests\Elsa.Hosts.SmokeTests.csproj", "{0BE4BC01-D02D-4185-A433-E33780584261}"
 EndProject
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "Elsa.Labels.UnitTests", "test\unit\Elsa.Labels.UnitTests\Elsa.Labels.UnitTests.csproj", "{ED8D7C78-154D-4124-8C0A-E63785A862E5}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -2468,6 +2471,18 @@ Global
 		{0BE4BC01-D02D-4185-A433-E33780584261}.Release|x64.Build.0 = Release|Any CPU
 		{0BE4BC01-D02D-4185-A433-E33780584261}.Release|x86.ActiveCfg = Release|Any CPU
 		{0BE4BC01-D02D-4185-A433-E33780584261}.Release|x86.Build.0 = Release|Any CPU
+		{ED8D7C78-154D-4124-8C0A-E63785A862E5}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{ED8D7C78-154D-4124-8C0A-E63785A862E5}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{ED8D7C78-154D-4124-8C0A-E63785A862E5}.Debug|x64.ActiveCfg = Debug|Any CPU
+		{ED8D7C78-154D-4124-8C0A-E63785A862E5}.Debug|x64.Build.0 = Debug|Any CPU
+		{ED8D7C78-154D-4124-8C0A-E63785A862E5}.Debug|x86.ActiveCfg = Debug|Any CPU
+		{ED8D7C78-154D-4124-8C0A-E63785A862E5}.Debug|x86.Build.0 = Debug|Any CPU
+		{ED8D7C78-154D-4124-8C0A-E63785A862E5}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{ED8D7C78-154D-4124-8C0A-E63785A862E5}.Release|Any CPU.Build.0 = Release|Any CPU
+		{ED8D7C78-154D-4124-8C0A-E63785A862E5}.Release|x64.ActiveCfg = Release|Any CPU
+		{ED8D7C78-154D-4124-8C0A-E63785A862E5}.Release|x64.Build.0 = Release|Any CPU
+		{ED8D7C78-154D-4124-8C0A-E63785A862E5}.Release|x86.ActiveCfg = Release|Any CPU
+		{ED8D7C78-154D-4124-8C0A-E63785A862E5}.Release|x86.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE
@@ -2673,6 +2688,7 @@ Global
 		{A4F3CB08-759D-4FE6-B715-E8D91E3E3F3E} = {AB07AAEB-2C7A-1088-880A-08DB82DA218D}
 		{0C16ED4D-2483-488D-9CA1-D269ED5BEB9F} = {18453B51-25EB-4317-A4B3-B10518252E92}
 		{0BE4BC01-D02D-4185-A433-E33780584261} = {90031D64-CA0F-46D0-9AF4-8DC023A5FFCD}
+		{ED8D7C78-154D-4124-8C0A-E63785A862E5} = {18453B51-25EB-4317-A4B3-B10518252E92}
 	EndGlobalSection
 	GlobalSection(ExtensibilityGlobals) = postSolution
 		SolutionGuid = {D4B5CEAA-7D70-4FCB-A68E-B03FBE5E0E5E}
diff --git a/src/modules/Elsa.Labels/Services/InMemoryLabelStore.cs b/src/modules/Elsa.Labels/Services/InMemoryLabelStore.cs
index 7afee7270..a5e64795f 100644
--- a/src/modules/Elsa.Labels/Services/InMemoryLabelStore.cs
+++ b/src/modules/Elsa.Labels/Services/InMemoryLabelStore.cs
@@ -1,4 +1,6 @@
+using Elsa.Common.Entities;
 using Elsa.Common.Models;
+using Elsa.Common.Multitenancy;
 using Elsa.Common.Services;
 using Elsa.Extensions;
 using Elsa.Labels.Contracts;
@@ -9,62 +11,92 @@ namespace Elsa.Labels.Services;
 /// <summary>
 /// An in-memory store of labels.
 /// </summary>
+/// <remarks>
+/// Ambient tenant is applied here rather than in callers.
+/// EF owns that via <c>SetTenantIdFilter</c> / <c>ApplyTenantId</c>; Memory must compensate.
+/// Labels contracts have no TenantAgnostic flag, so isolation always applies (EF query filter).
+/// </remarks>
 public class InMemoryLabelStore : ILabelStore
 {
     private readonly MemoryStore<Label> _labelStore;
     private readonly MemoryStore<WorkflowDefinitionLabel> _workflowDefinitionLabelStore;
+    private readonly ITenantAccessor? _tenantAccessor;
 
     /// <summary>
     /// Constructor.
     /// </summary>
-    public InMemoryLabelStore(MemoryStore<Label> labelStore, MemoryStore<WorkflowDefinitionLabel> workflowDefinitionLabelStore)
+    public InMemoryLabelStore(
+        MemoryStore<Label> labelStore,
+        MemoryStore<WorkflowDefinitionLabel> workflowDefinitionLabelStore,
+        ITenantAccessor? tenantAccessor = null)
     {
         _labelStore = labelStore;
         _workflowDefinitionLabelStore = workflowDefinitionLabelStore;
+        _tenantAccessor = tenantAccessor;
     }
 
     /// <inheritdoc />
     public Task SaveAsync(Label record, CancellationToken cancellationToken = default)
     {
-        _labelStore.Save(record, x => x.Id);
+        ApplyCurrentTenant(record);
+        lock (_labelStore.Sync)
+            _labelStore.Save(record, x => x.Id);
         return Task.CompletedTask;
     }
 
     /// <inheritdoc />
     public Task SaveManyAsync(IEnumerable<Label> records, CancellationToken cancellationToken = default)
     {
-        _labelStore.SaveMany(records, x => x.Id);
+        var list = records.ToList();
+
+        foreach (var record in list)
+            ApplyCurrentTenant(record);
+
+        lock (_labelStore.Sync)
+            _labelStore.SaveMany(list, x => x.Id);
         return Task.CompletedTask;
     }
 
     /// <inheritdoc />
     public Task<bool> DeleteAsync(string id, CancellationToken cancellationToken = default)
     {
-        _workflowDefinitionLabelStore.DeleteWhere(x => x.LabelId == id);
-        var result = _labelStore.Delete(id);
-        return Task.FromResult(result);
+        lock (_labelStore.Sync)
+        lock (_workflowDefinitionLabelStore.Sync)
+        {
+            var deleted = _labelStore.DeleteWhere(x => x.Id == id && IsVisible(x));
+
+            if (deleted == 0)
+                return Task.FromResult(false);
+
+            _workflowDefinitionLabelStore.DeleteWhere(x => x.LabelId == id && IsVisible(x));
+            return Task.FromResult(true);
+        }
     }
 
     /// <inheritdoc />
     public Task<long> DeleteManyAsync(IEnumerable<string> ids, CancellationToken cancellationToken = default)
     {
         var idList = ids.ToList();
-        _workflowDefinitionLabelStore.DeleteWhere(x => idList.Contains(x.LabelId));
-        var result = _labelStore.DeleteMany(idList);
-        return Task.FromResult(result);
+
+        lock (_labelStore.Sync)
+        lock (_workflowDefinitionLabelStore.Sync)
+        {
+            var deleted = _labelStore.DeleteWhere(x => idList.Contains(x.Id) && IsVisible(x));
+            _workflowDefinitionLabelStore.DeleteWhere(x => idList.Contains(x.LabelId) && IsVisible(x));
+            return Task.FromResult(deleted);
+        }
     }
 
     /// <inheritdoc />
     public Task<Label?> FindByIdAsync(string id, CancellationToken cancellationToken = default)
     {
-        var record = _labelStore.Find(x => x.Id == id);
-        return Task.FromResult(record);
+        return Task.FromResult(FindVisibleLabel(id));
     }
 
     /// <inheritdoc />
     public Task<Page<Label>> ListAsync(PageArgs? pageArgs = default, CancellationToken cancellationToken = default)
     {
-        var query = _labelStore.List().AsQueryable().OrderBy(x => x.Name);
+        var query = _labelStore.List().AsQueryable().WhereVisibleToTenant(CurrentTenantId).OrderBy(x => x.Name);
         var page = query.ToPage(pageArgs);
         return Task.FromResult(page);
     }
@@ -73,6 +105,22 @@ public class InMemoryLabelStore : ILabelStore
     public Task<IEnumerable<Label>> FindManyByIdAsync(IEnumerable<string> ids, CancellationToken cancellationToken)
     {
         var idList = ids.ToList();
-        return Task.FromResult(_labelStore.FindMany(x => idList.Contains(x.Id)));
+        var records = _labelStore.Query(query => query.WhereVisibleToTenant(CurrentTenantId).Where(x => idList.Contains(x.Id)));
+        return Task.FromResult(records);
     }
-}
\ No newline at end of file
+
+    private Label? FindVisibleLabel(string id) =>
+        _labelStore.Query(query => query.WhereVisibleToTenant(CurrentTenantId).Where(x => x.Id == id)).FirstOrDefault();
+
+    private bool IsVisible(Entity entity) => TenantVisibility.IsVisible(entity.TenantId, CurrentTenantId);
+
+    private string CurrentTenantId => _tenantAccessor?.TenantId ?? Tenant.DefaultTenantId;
+
+    private void ApplyCurrentTenant(Entity entity)
+    {
+        if (entity.TenantId == Tenant.AgnosticTenantId || _tenantAccessor is null)
+            return;
+
+        entity.TenantId ??= _tenantAccessor.TenantId;
+    }
+}
diff --git a/src/modules/Elsa.Labels/Services/InMemoryWorkflowDefinitionLabelStore.cs b/src/modules/Elsa.Labels/Services/InMemoryWorkflowDefinitionLabelStore.cs
index 943ab5110..44eeed0e3 100644
--- a/src/modules/Elsa.Labels/Services/InMemoryWorkflowDefinitionLabelStore.cs
+++ b/src/modules/Elsa.Labels/Services/InMemoryWorkflowDefinitionLabelStore.cs
@@ -1,3 +1,5 @@
+using Elsa.Common.Entities;
+using Elsa.Common.Multitenancy;
 using Elsa.Common.Services;
 using Elsa.Labels.Contracts;
 using Elsa.Labels.Entities;
@@ -7,43 +9,58 @@ namespace Elsa.Labels.Services;
 /// <summary>
 /// An in-memory store of workflow-label associations.
 /// </summary>
+/// <remarks>
+/// Ambient tenant is applied here rather than in callers.
+/// EF owns that via <c>SetTenantIdFilter</c> / <c>ApplyTenantId</c>; Memory must compensate.
+/// Labels contracts have no TenantAgnostic flag, so isolation always applies (EF query filter).
+/// </remarks>
 public class InMemoryWorkflowDefinitionLabelStore : IWorkflowDefinitionLabelStore, IWorkflowDefinitionLabelQuery
 {
     private readonly MemoryStore<WorkflowDefinitionLabel> _store;
+    private readonly ITenantAccessor? _tenantAccessor;
 
     /// <summary>
     /// Constructor.
     /// </summary>
-    public InMemoryWorkflowDefinitionLabelStore(MemoryStore<WorkflowDefinitionLabel> store)
+    public InMemoryWorkflowDefinitionLabelStore(MemoryStore<WorkflowDefinitionLabel> store, ITenantAccessor? tenantAccessor = null)
     {
         _store = store;
+        _tenantAccessor = tenantAccessor;
     }
 
     /// <inheritdoc />
     public Task SaveAsync(WorkflowDefinitionLabel record, CancellationToken cancellationToken = default)
     {
-        _store.Save(record, x => x.Id);
+        ApplyCurrentTenant(record);
+        lock (_store.Sync)
+            _store.Save(record, x => x.Id);
         return Task.CompletedTask;
     }
 
     /// <inheritdoc />
     public Task SaveManyAsync(IEnumerable<WorkflowDefinitionLabel> records, CancellationToken cancellationToken = default)
     {
-        _store.SaveMany(records, x => x.Id);
+        var list = records.ToList();
+
+        foreach (var record in list)
+            ApplyCurrentTenant(record);
+
+        lock (_store.Sync)
+            _store.SaveMany(list, x => x.Id);
         return Task.CompletedTask;
     }
 
     /// <inheritdoc />
     public Task<bool> DeleteAsync(string id, CancellationToken cancellationToken = default)
     {
-        var result = _store.Delete(id);
-        return Task.FromResult(result);
+        lock (_store.Sync)
+            return Task.FromResult(_store.DeleteWhere(x => x.Id == id && IsVisible(x)) > 0);
     }
-    
+
     /// <inheritdoc />
     public Task<IEnumerable<WorkflowDefinitionLabel>> FindByWorkflowDefinitionVersionIdAsync(string workflowDefinitionVersionId, CancellationToken cancellationToken = default)
     {
-        var result = _store.FindMany(x => x.WorkflowDefinitionVersionId == workflowDefinitionVersionId);
+        var result = _store.Query(query => query.WhereVisibleToTenant(CurrentTenantId).Where(x => x.WorkflowDefinitionVersionId == workflowDefinitionVersionId));
         return Task.FromResult(result);
     }
 
@@ -51,52 +68,67 @@ public class InMemoryWorkflowDefinitionLabelStore : IWorkflowDefinitionLabelStor
     public Task<IEnumerable<WorkflowDefinitionLabel>> FindByLabelIdsAsync(IEnumerable<string> labelIds, CancellationToken cancellationToken = default)
     {
         var ids = labelIds.ToHashSet();
-        var result = _store.FindMany(x => ids.Contains(x.LabelId));
+        var result = _store.Query(query => query.WhereVisibleToTenant(CurrentTenantId).Where(x => ids.Contains(x.LabelId)));
         return Task.FromResult(result);
     }
 
     /// <inheritdoc />
     public Task ReplaceAsync(IEnumerable<WorkflowDefinitionLabel> removed, IEnumerable<WorkflowDefinitionLabel> added, CancellationToken cancellationToken = default)
     {
-        _store.DeleteMany(removed, x => x.Id);
-        _store.SaveMany(added, x => x.Id);
+        var removedIds = removed.Select(x => x.Id).ToHashSet();
+        var addedList = added.ToList();
+
+        foreach (var record in addedList)
+            ApplyCurrentTenant(record);
+
+        lock (_store.Sync)
+        {
+            _store.DeleteWhere(x => removedIds.Contains(x.Id) && IsVisible(x));
+            _store.SaveMany(addedList, x => x.Id);
+        }
+
         return Task.CompletedTask;
     }
 
     /// <inheritdoc />
     public Task<long> DeleteByWorkflowDefinitionIdAsync(string workflowDefinitionId, CancellationToken cancellationToken = default)
     {
-        var result = _store.DeleteWhere(x => x.WorkflowDefinitionId == workflowDefinitionId);
-        return Task.FromResult(result);
+        lock (_store.Sync)
+            return Task.FromResult(_store.DeleteWhere(x => x.WorkflowDefinitionId == workflowDefinitionId && IsVisible(x)));
     }
 
     /// <inheritdoc />
     public Task<long> DeleteByWorkflowDefinitionVersionIdAsync(string workflowDefinitionVersionId, CancellationToken cancellationToken = default)
     {
-        var result = _store.DeleteWhere(x => x.WorkflowDefinitionVersionId == workflowDefinitionVersionId);
-        return Task.FromResult(result);
+        lock (_store.Sync)
+            return Task.FromResult(_store.DeleteWhere(x => x.WorkflowDefinitionVersionId == workflowDefinitionVersionId && IsVisible(x)));
     }
 
     /// <inheritdoc />
     public Task<long> DeleteByWorkflowDefinitionIdsAsync(IEnumerable<string> workflowDefinitionIds, CancellationToken cancellationToken = default)
     {
         var ids = workflowDefinitionIds.ToList();
-        var result = _store.DeleteWhere(x => ids.Contains(x.WorkflowDefinitionId));
-        return Task.FromResult(result);
+        lock (_store.Sync)
+            return Task.FromResult(_store.DeleteWhere(x => ids.Contains(x.WorkflowDefinitionId) && IsVisible(x)));
     }
 
     /// <inheritdoc />
     public Task<long> DeleteByWorkflowDefinitionVersionIdsAsync(IEnumerable<string> workflowDefinitionVersionIds, CancellationToken cancellationToken = default)
     {
         var ids = workflowDefinitionVersionIds.ToList();
-        var result = _store.DeleteWhere(x => ids.Contains(x.WorkflowDefinitionVersionId));
-        return Task.FromResult(result);
-    }
-    
-    private Task<long> DeleteManyAsync(IEnumerable<string> ids, CancellationToken cancellationToken = default)
-    {
-        var result = _store.DeleteMany(ids);
-        return Task.FromResult(result);
+        lock (_store.Sync)
+            return Task.FromResult(_store.DeleteWhere(x => ids.Contains(x.WorkflowDefinitionVersionId) && IsVisible(x)));
     }
 
-}
\ No newline at end of file
+    private bool IsVisible(Entity entity) => TenantVisibility.IsVisible(entity.TenantId, CurrentTenantId);
+
+    private string CurrentTenantId => _tenantAccessor?.TenantId ?? Tenant.DefaultTenantId;
+
+    private void ApplyCurrentTenant(Entity entity)
+    {
+        if (entity.TenantId == Tenant.AgnosticTenantId || _tenantAccessor is null)
+            return;
+
+        entity.TenantId ??= _tenantAccessor.TenantId;
+    }
+}
diff --git a/test/unit/Elsa.Labels.UnitTests/Elsa.Labels.UnitTests.csproj b/test/unit/Elsa.Labels.UnitTests/Elsa.Labels.UnitTests.csproj
new file mode 100644
index 000000000..83e0d07b0
--- /dev/null
+++ b/test/unit/Elsa.Labels.UnitTests/Elsa.Labels.UnitTests.csproj
@@ -0,0 +1,12 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+    <PropertyGroup>
+        <Include>[Elsa.Labels]*</Include>
+    </PropertyGroup>
+
+    <ItemGroup>
+        <ProjectReference Include="..\..\..\src\common\Elsa.Testing.Shared\Elsa.Testing.Shared.csproj" />
+        <ProjectReference Include="..\..\..\src\modules\Elsa.Labels\Elsa.Labels.csproj" />
+    </ItemGroup>
+
+</Project>
diff --git a/test/unit/Elsa.Labels.UnitTests/Services/InMemoryLabelStoreTenantIsolationTests.cs b/test/unit/Elsa.Labels.UnitTests/Services/InMemoryLabelStoreTenantIsolationTests.cs
new file mode 100644
index 000000000..0f5ced79b
--- /dev/null
+++ b/test/unit/Elsa.Labels.UnitTests/Services/InMemoryLabelStoreTenantIsolationTests.cs
@@ -0,0 +1,188 @@
+using Elsa.Common.Multitenancy;
+using Elsa.Common.Services;
+using Elsa.Labels.Entities;
+using Elsa.Labels.Services;
+using Elsa.Testing.Shared.Multitenancy;
+
+namespace Elsa.Labels.UnitTests.Services;
+
+/// <summary>
+/// Memory Labels must honor ambient tenant the same way EF does via
+/// <c>SetTenantIdFilter</c> / <c>ApplyTenantId</c>. Contracts have no TenantAgnostic flag.
+/// </summary>
+public class InMemoryLabelStoreTenantIsolationTests
+{
+    [Fact(DisplayName = "ListAsync hides other tenants and keeps * visible")]
+    public async Task ListAsync_HidesOtherTenants()
+    {
+        var store = CreateStore("tenant-a");
+        await SeedMixedTenantsAsync(store);
+
+        var found = (await store.ListAsync()).Items.ToList();
+
+        Assert.Equal(2, found.Count);
+        Assert.Contains(found, x => x.Id == "label-a");
+        Assert.Contains(found, x => x.Id == "label-star");
+        Assert.DoesNotContain(found, x => x.Id == "label-b");
+    }
+
+    [Fact(DisplayName = "FindByIdAsync does not return another tenant's row")]
+    public async Task FindByIdAsync_WhenOtherTenant_ReturnsNull()
+    {
+        var store = CreateStore("tenant-a");
+        await SeedMixedTenantsAsync(store);
+
+        var found = await store.FindByIdAsync("label-b");
+
+        Assert.Null(found);
+    }
+
+    [Fact(DisplayName = "FindManyByIdAsync hides other tenants")]
+    public async Task FindManyByIdAsync_HidesOtherTenants()
+    {
+        var store = CreateStore("tenant-a");
+        await SeedMixedTenantsAsync(store);
+
+        var found = (await store.FindManyByIdAsync(["label-a", "label-b", "label-star"], CancellationToken.None)).ToList();
+
+        Assert.Equal(2, found.Count);
+        Assert.Contains(found, x => x.Id == "label-a");
+        Assert.Contains(found, x => x.Id == "label-star");
+        Assert.DoesNotContain(found, x => x.Id == "label-b");
+    }
+
+    [Fact(DisplayName = "DeleteAsync does not remove another tenant's rows or associations")]
+    public async Task DeleteAsync_DoesNotDeleteOtherTenantRows()
+    {
+        var labels = new MemoryStore<Label>();
+        var associations = new MemoryStore<WorkflowDefinitionLabel>();
+        var tenantA = new InMemoryLabelStore(labels, associations, new TestTenantAccessor("tenant-a"));
+        var tenantB = new InMemoryLabelStore(labels, associations, new TestTenantAccessor("tenant-b"));
+        var tenantBAssociations = new InMemoryWorkflowDefinitionLabelStore(associations, new TestTenantAccessor("tenant-b"));
+        await SeedMixedTenantsAsync(tenantA);
+        await tenantBAssociations.SaveAsync(Association("assoc-b", "label-b", "tenant-b"));
+
+        var deleted = await tenantA.DeleteAsync("label-b");
+        var remainingForB = await tenantB.FindByIdAsync("label-b");
+        var remainingAssociations = (await tenantBAssociations.FindByLabelIdsAsync(["label-b"])).ToList();
+
+        Assert.False(deleted);
+        Assert.NotNull(remainingForB);
+        Assert.Equal("label-b", remainingForB.Id);
+        Assert.Single(remainingAssociations);
+        Assert.Equal("assoc-b", remainingAssociations[0].Id);
+    }
+
+    [Fact(DisplayName = "DeleteManyAsync does not wipe other tenants' rows")]
+    public async Task DeleteManyAsync_DoesNotWipeOtherTenantRows()
+    {
+        var labels = new MemoryStore<Label>();
+        var associations = new MemoryStore<WorkflowDefinitionLabel>();
+        var tenantA = new InMemoryLabelStore(labels, associations, new TestTenantAccessor("tenant-a"));
+        var tenantB = new InMemoryLabelStore(labels, associations, new TestTenantAccessor("tenant-b"));
+        await SeedMixedTenantsAsync(tenantA);
+
+        var deleted = await tenantA.DeleteManyAsync(["label-a", "label-b", "label-star"]);
+        var remainingForA = (await tenantA.ListAsync()).Items.ToList();
+        var remainingForB = await tenantB.FindByIdAsync("label-b");
+
+        Assert.Equal(2, deleted);
+        Assert.Empty(remainingForA);
+        Assert.NotNull(remainingForB);
+        Assert.Equal("label-b", remainingForB.Id);
+    }
+
+    [Fact(DisplayName = "DeleteAsync leaves a same-ID row after another tenant replaces it")]
+    public async Task DeleteAsync_WhenSameIdWasReplacedByOtherTenant_LeavesReplacement()
+    {
+        var labels = new MemoryStore<Label>();
+        var associations = new MemoryStore<WorkflowDefinitionLabel>();
+        var tenantA = new InMemoryLabelStore(labels, associations, new TestTenantAccessor("tenant-a"));
+        var tenantB = new InMemoryLabelStore(labels, associations, new TestTenantAccessor("tenant-b"));
+        await tenantA.SaveAsync(new Label { Id = "shared", Name = "A", TenantId = "tenant-a" });
+        await tenantB.SaveAsync(new Label { Id = "shared", Name = "B", TenantId = "tenant-b" });
+
+        var deleted = await tenantA.DeleteAsync("shared");
+        var remaining = await tenantB.FindByIdAsync("shared");
+
+        Assert.False(deleted);
+        Assert.NotNull(remaining);
+        Assert.Equal("tenant-b", remaining.TenantId);
+    }
+
+    [Fact(DisplayName = "SaveAsync stamps the ambient tenant when TenantId is unset")]
+    public async Task SaveAsync_WhenTenantIdUnset_StampsAmbientTenant()
+    {
+        var store = CreateStore("tenant-a");
+        var label = new Label { Id = "label-new", Name = "New" };
+
+        await store.SaveAsync(label);
+
+        Assert.Equal("tenant-a", label.TenantId);
+        Assert.Equal("tenant-a", (await store.FindByIdAsync("label-new"))!.TenantId);
+    }
+
+    [Fact(DisplayName = "SaveAsync does not overwrite * or an explicit TenantId")]
+    public async Task SaveAsync_DoesNotOverwriteAgnosticOrExplicitTenantId()
+    {
+        var store = CreateStore("tenant-a");
+        var agnostic = new Label { Id = "label-star", Name = "Star", TenantId = Tenant.AgnosticTenantId };
+        var explicitTenant = new Label { Id = "label-a", Name = "A", TenantId = "tenant-a" };
+
+        await store.SaveAsync(agnostic);
+        await store.SaveAsync(explicitTenant);
+
+        Assert.Equal(Tenant.AgnosticTenantId, agnostic.TenantId);
+        Assert.Equal("tenant-a", explicitTenant.TenantId);
+    }
+
+    [Fact(DisplayName = "ListAsync on the default tenant includes null TenantId rows")]
+    public async Task ListAsync_WhenAmbientIsDefault_IncludesNullTenantId()
+    {
+        var store = StoreWithPreassignedRows(Tenant.DefaultTenantId);
+
+        var found = (await store.ListAsync()).Items.ToList();
+
+        Assert.Single(found);
+        Assert.Equal("label-null", found[0].Id);
+    }
+
+    [Fact(DisplayName = "ListAsync on a named tenant hides null TenantId rows")]
+    public async Task ListAsync_WhenAmbientIsNamed_HidesNullTenantId()
+    {
+        var store = StoreWithPreassignedRows("tenant-a");
+
+        var found = (await store.ListAsync()).Items.ToList();
+
+        Assert.Single(found);
+        Assert.Equal("label-a", found[0].Id);
+    }
+
+    private static InMemoryLabelStore CreateStore(string tenantId) =>
+        new(new MemoryStore<Label>(), new MemoryStore<WorkflowDefinitionLabel>(), new TestTenantAccessor(tenantId));
+
+    private static InMemoryLabelStore StoreWithPreassignedRows(string ambientTenantId)
+    {
+        var labels = new MemoryStore<Label>();
+        labels.Save(new Label { Id = "label-null", Name = "Null", TenantId = null }, x => x.Id);
+        labels.Save(new Label { Id = "label-a", Name = "A", TenantId = "tenant-a" }, x => x.Id);
+        return new InMemoryLabelStore(labels, new MemoryStore<WorkflowDefinitionLabel>(), new TestTenantAccessor(ambientTenantId));
+    }
+
+    private static async Task SeedMixedTenantsAsync(InMemoryLabelStore store)
+    {
+        await store.SaveAsync(new Label { Id = "label-a", Name = "A", TenantId = "tenant-a" });
+        await store.SaveAsync(new Label { Id = "label-b", Name = "B", TenantId = "tenant-b" });
+        await store.SaveAsync(new Label { Id = "label-star", Name = "Star", TenantId = Tenant.AgnosticTenantId });
+    }
+
+    private static WorkflowDefinitionLabel Association(string id, string labelId, string tenantId) =>
+        new()
+        {
+            Id = id,
+            LabelId = labelId,
+            WorkflowDefinitionId = "order",
+            WorkflowDefinitionVersionId = "order:1",
+            TenantId = tenantId
+        };
+}
diff --git a/test/unit/Elsa.Labels.UnitTests/Services/InMemoryWorkflowDefinitionLabelStoreTenantIsolationTests.cs b/test/unit/Elsa.Labels.UnitTests/Services/InMemoryWorkflowDefinitionLabelStoreTenantIsolationTests.cs
new file mode 100644
index 000000000..b60b5cede
--- /dev/null
+++ b/test/unit/Elsa.Labels.UnitTests/Services/InMemoryWorkflowDefinitionLabelStoreTenantIsolationTests.cs
@@ -0,0 +1,166 @@
+using Elsa.Common.Multitenancy;
+using Elsa.Common.Services;
+using Elsa.Labels.Entities;
+using Elsa.Labels.Services;
+using Elsa.Testing.Shared.Multitenancy;
+
+namespace Elsa.Labels.UnitTests.Services;
+
+/// <summary>
+/// Memory workflow-definition labels must honor ambient tenant the same way EF does via
+/// <c>SetTenantIdFilter</c> / <c>ApplyTenantId</c>. Contracts have no TenantAgnostic flag.
+/// </summary>
+public class InMemoryWorkflowDefinitionLabelStoreTenantIsolationTests
+{
+    [Fact(DisplayName = "FindByWorkflowDefinitionVersionIdAsync hides other tenants and keeps * visible")]
+    public async Task FindByWorkflowDefinitionVersionIdAsync_HidesOtherTenants()
+    {
+        var store = CreateStore("tenant-a");
+        await SeedMixedTenantsAsync(store);
+
+        var found = (await store.FindByWorkflowDefinitionVersionIdAsync("order:1")).ToList();
+
+        Assert.Equal(2, found.Count);
+        Assert.Contains(found, x => x.Id == "assoc-a");
+        Assert.Contains(found, x => x.Id == "assoc-star");
+        Assert.DoesNotContain(found, x => x.Id == "assoc-b");
+    }
+
+    [Fact(DisplayName = "FindByLabelIdsAsync hides other tenants")]
+    public async Task FindByLabelIdsAsync_HidesOtherTenants()
+    {
+        var store = CreateStore("tenant-a");
+        await SeedMixedTenantsAsync(store);
+
+        var found = (await store.FindByLabelIdsAsync(["red"])).ToList();
+
+        Assert.Equal(2, found.Count);
+        Assert.Contains(found, x => x.Id == "assoc-a");
+        Assert.Contains(found, x => x.Id == "assoc-star");
+        Assert.DoesNotContain(found, x => x.Id == "assoc-b");
+    }
+
+    [Fact(DisplayName = "DeleteAsync does not remove another tenant's row")]
+    public async Task DeleteAsync_DoesNotDeleteOtherTenantRows()
+    {
+        var backing = new MemoryStore<WorkflowDefinitionLabel>();
+        var tenantA = new InMemoryWorkflowDefinitionLabelStore(backing, new TestTenantAccessor("tenant-a"));
+        var tenantB = new InMemoryWorkflowDefinitionLabelStore(backing, new TestTenantAccessor("tenant-b"));
+        await SeedMixedTenantsAsync(tenantA);
+
+        var deleted = await tenantA.DeleteAsync("assoc-b");
+        var remainingForB = (await tenantB.FindByLabelIdsAsync(["red"])).ToList();
+
+        Assert.False(deleted);
+        Assert.Contains(remainingForB, x => x.Id == "assoc-b");
+        Assert.Contains(remainingForB, x => x.Id == "assoc-star");
+        Assert.DoesNotContain(remainingForB, x => x.Id == "assoc-a");
+    }
+
+    [Fact(DisplayName = "DeleteAsync leaves a same-ID row after another tenant replaces it")]
+    public async Task DeleteAsync_WhenSameIdWasReplacedByOtherTenant_LeavesReplacement()
+    {
+        var backing = new MemoryStore<WorkflowDefinitionLabel>();
+        var tenantA = new InMemoryWorkflowDefinitionLabelStore(backing, new TestTenantAccessor("tenant-a"));
+        var tenantB = new InMemoryWorkflowDefinitionLabelStore(backing, new TestTenantAccessor("tenant-b"));
+        await tenantA.SaveAsync(Association("shared", "tenant-a"));
+        await tenantB.SaveAsync(Association("shared", "tenant-b"));
+
+        var deleted = await tenantA.DeleteAsync("shared");
+        var remaining = (await tenantB.FindByLabelIdsAsync(["red"])).ToList();
+
+        Assert.False(deleted);
+        Assert.Single(remaining);
+        Assert.Equal("shared", remaining[0].Id);
+        Assert.Equal("tenant-b", remaining[0].TenantId);
+    }
+
+    [Fact(DisplayName = "DeleteByWorkflowDefinitionIdAsync leaves the other tenant's associations")]
+    public async Task DeleteByWorkflowDefinitionIdAsync_WhenDefinitionIdIsShared_LeavesOtherTenantRows()
+    {
+        var backing = new MemoryStore<WorkflowDefinitionLabel>();
+        var tenantA = new InMemoryWorkflowDefinitionLabelStore(backing, new TestTenantAccessor("tenant-a"));
+        var tenantB = new InMemoryWorkflowDefinitionLabelStore(backing, new TestTenantAccessor("tenant-b"));
+        await tenantA.SaveAsync(Association("assoc-a", "tenant-a"));
+        await tenantB.SaveAsync(Association("assoc-b", "tenant-b"));
+
+        var deleted = await tenantA.DeleteByWorkflowDefinitionIdAsync("order");
+        var remainingForA = (await tenantA.FindByWorkflowDefinitionVersionIdAsync("order:1")).ToList();
+        var remainingForB = (await tenantB.FindByWorkflowDefinitionVersionIdAsync("order:1")).ToList();
+
+        Assert.Equal(1, deleted);
+        Assert.Empty(remainingForA);
+        Assert.Single(remainingForB);
+        Assert.Equal("assoc-b", remainingForB[0].Id);
+    }
+
+    [Fact(DisplayName = "ReplaceAsync does not delete another tenant's rows")]
+    public async Task ReplaceAsync_DoesNotDeleteOtherTenantRows()
+    {
+        var backing = new MemoryStore<WorkflowDefinitionLabel>();
+        var tenantA = new InMemoryWorkflowDefinitionLabelStore(backing, new TestTenantAccessor("tenant-a"));
+        var tenantB = new InMemoryWorkflowDefinitionLabelStore(backing, new TestTenantAccessor("tenant-b"));
+        await SeedMixedTenantsAsync(tenantA);
+
+        await tenantA.ReplaceAsync(
+            [Association("assoc-a", "tenant-a"), Association("assoc-b", "tenant-b")],
+            [Association("assoc-a2", "tenant-a")]);
+
+        var remainingForA = (await tenantA.FindByWorkflowDefinitionVersionIdAsync("order:1")).ToList();
+        var remainingForB = (await tenantB.FindByLabelIdsAsync(["red"])).ToList();
+
+        Assert.Contains(remainingForA, x => x.Id == "assoc-a2");
+        Assert.Contains(remainingForA, x => x.Id == "assoc-star");
+        Assert.DoesNotContain(remainingForA, x => x.Id == "assoc-a");
+        Assert.Contains(remainingForB, x => x.Id == "assoc-b");
+        Assert.Contains(remainingForB, x => x.Id == "assoc-star");
+        Assert.DoesNotContain(remainingForB, x => x.Id == "assoc-a");
+    }
+
+    [Fact(DisplayName = "SaveAsync stamps the ambient tenant when TenantId is unset")]
+    public async Task SaveAsync_WhenTenantIdUnset_StampsAmbientTenant()
+    {
+        var store = CreateStore("tenant-a");
+        var association = Association("assoc-new", tenantId: null);
+
+        await store.SaveAsync(association);
+
+        Assert.Equal("tenant-a", association.TenantId);
+        var found = (await store.FindByLabelIdsAsync(["red"])).Single();
+        Assert.Equal("tenant-a", found.TenantId);
+    }
+
+    [Fact(DisplayName = "FindByLabelIdsAsync on the default tenant includes null TenantId rows")]
+    public async Task FindByLabelIdsAsync_WhenAmbientIsDefault_IncludesNullTenantId()
+    {
+        var backing = new MemoryStore<WorkflowDefinitionLabel>();
+        backing.Save(Association("assoc-null", tenantId: null), x => x.Id);
+        backing.Save(Association("assoc-a", "tenant-a"), x => x.Id);
+        var store = new InMemoryWorkflowDefinitionLabelStore(backing, new TestTenantAccessor(Tenant.DefaultTenantId));
+
+        var found = (await store.FindByLabelIdsAsync(["red"])).ToList();
+
+        Assert.Single(found);
+        Assert.Equal("assoc-null", found[0].Id);
+    }
+
+    private static InMemoryWorkflowDefinitionLabelStore CreateStore(string tenantId) =>
+        new(new MemoryStore<WorkflowDefinitionLabel>(), new TestTenantAccessor(tenantId));
+
+    private static async Task SeedMixedTenantsAsync(InMemoryWorkflowDefinitionLabelStore store)
+    {
+        await store.SaveAsync(Association("assoc-a", "tenant-a"));
+        await store.SaveAsync(Association("assoc-b", "tenant-b"));
+        await store.SaveAsync(Association("assoc-star", Tenant.AgnosticTenantId));
+    }
+
+    private static WorkflowDefinitionLabel Association(string id, string? tenantId) =>
+        new()
+        {
+            Id = id,
+            LabelId = "red",
+            WorkflowDefinitionId = "order",
+            WorkflowDefinitionVersionId = "order:1",
+            TenantId = tenantId
+        };
+}