diff --git a/test/Api.Test/Controllers/CollectionsControllerTests.cs b/test/Api.Test/Controllers/CollectionsControllerTests.cs
index 196569acb3..9e3db4741a 100644
--- a/test/Api.Test/Controllers/CollectionsControllerTests.cs
+++ b/test/Api.Test/Controllers/CollectionsControllerTests.cs
@@ -2,6 +2,7 @@
 using Bit.Api.Controllers;
 using Bit.Api.Models.Request;
 using Bit.Api.Vault.AuthorizationHandlers.Collections;
+using Bit.Core;
 using Bit.Core.Context;
 using Bit.Core.Entities;
 using Bit.Core.Exceptions;
@@ -25,6 +26,8 @@ public class CollectionsControllerTests
     public async Task Post_Success(Guid orgId, CollectionRequestModel collectionRequest,
         SutProvider<CollectionsController> sutProvider)
     {
+        sutProvider.EnableFeatureFlag(FeatureFlagKeys.FlexibleCollections);
+
         Collection ExpectedCollection() => Arg.Is<Collection>(c =>
             c.Name == collectionRequest.Name && c.ExternalId == collectionRequest.ExternalId &&
             c.OrganizationId == orgId);
@@ -47,6 +50,7 @@ public class CollectionsControllerTests
     public async Task Put_Success(Guid orgId, Guid collectionId, Guid userId, CollectionRequestModel collectionRequest,
         SutProvider<CollectionsController> sutProvider)
     {
+        sutProvider.EnableFeatureFlag(FeatureFlagKeys.FlexibleCollections);
         sutProvider.GetDependency<ICurrentContext>()
             .ViewAssignedCollections(orgId)
             .Returns(true);
@@ -73,6 +77,7 @@ public class CollectionsControllerTests
     public async Task Put_CanNotEditAssignedCollection_ThrowsNotFound(Guid orgId, Guid collectionId, Guid userId, CollectionRequestModel collectionRequest,
         SutProvider<CollectionsController> sutProvider)
     {
+        sutProvider.EnableFeatureFlag(FeatureFlagKeys.FlexibleCollections);
         sutProvider.GetDependency<ICurrentContext>()
             .EditAssignedCollections(orgId)
             .Returns(true);
@@ -91,6 +96,7 @@ public class CollectionsControllerTests
     [Theory, BitAutoData]
     public async Task GetOrganizationCollectionsWithGroups_NoManagerPermissions_ThrowsNotFound(Organization organization, SutProvider<CollectionsController> sutProvider)
     {
+        sutProvider.EnableFeatureFlag(FeatureFlagKeys.FlexibleCollections);
         sutProvider.GetDependency<ICurrentContext>().ViewAssignedCollections(organization.Id).Returns(false);
 
         await Assert.ThrowsAsync<NotFoundException>(() => sutProvider.Sut.GetManyWithDetails(organization.Id));
@@ -101,6 +107,7 @@ public class CollectionsControllerTests
     [Theory, BitAutoData]
     public async Task GetOrganizationCollectionsWithGroups_AdminPermissions_GetsAllCollections(Organization organization, User user, SutProvider<CollectionsController> sutProvider)
     {
+        sutProvider.EnableFeatureFlag(FeatureFlagKeys.FlexibleCollections);
         sutProvider.GetDependency<ICurrentContext>().UserId.Returns(user.Id);
         sutProvider.GetDependency<ICurrentContext>().ViewAllCollections(organization.Id).Returns(true);
         sutProvider.GetDependency<ICurrentContext>().OrganizationAdmin(organization.Id).Returns(true);
@@ -114,6 +121,7 @@ public class CollectionsControllerTests
     [Theory, BitAutoData]
     public async Task GetOrganizationCollectionsWithGroups_MissingViewAllPermissions_GetsAssignedCollections(Organization organization, User user, SutProvider<CollectionsController> sutProvider)
     {
+        sutProvider.EnableFeatureFlag(FeatureFlagKeys.FlexibleCollections);
         sutProvider.GetDependency<ICurrentContext>().UserId.Returns(user.Id);
         sutProvider.GetDependency<ICurrentContext>().ViewAssignedCollections(organization.Id).Returns(true);
         sutProvider.GetDependency<ICurrentContext>().OrganizationManager(organization.Id).Returns(true);
@@ -127,6 +135,7 @@ public class CollectionsControllerTests
     [Theory, BitAutoData]
     public async Task GetOrganizationCollectionsWithGroups_CustomUserWithManagerPermissions_GetsAssignedCollections(Organization organization, User user, SutProvider<CollectionsController> sutProvider)
     {
+        sutProvider.EnableFeatureFlag(FeatureFlagKeys.FlexibleCollections);
         sutProvider.GetDependency<ICurrentContext>().UserId.Returns(user.Id);
         sutProvider.GetDependency<ICurrentContext>().ViewAssignedCollections(organization.Id).Returns(true);
         sutProvider.GetDependency<ICurrentContext>().EditAssignedCollections(organization.Id).Returns(true);
@@ -142,6 +151,7 @@ public class CollectionsControllerTests
     [Theory, BitAutoData]
     public async Task DeleteMany_Success(Guid orgId, Collection collection1, Collection collection2, SutProvider<CollectionsController> sutProvider)
     {
+        sutProvider.EnableFeatureFlag(FeatureFlagKeys.FlexibleCollections);
         // Arrange
         var model = new CollectionBulkDeleteRequestModel
         {
@@ -184,6 +194,7 @@ public class CollectionsControllerTests
     [Theory, BitAutoData]
     public async Task DeleteMany_PermissionDenied_ThrowsNotFound(Guid orgId, Collection collection1, Collection collection2, SutProvider<CollectionsController> sutProvider)
     {
+        sutProvider.EnableFeatureFlag(FeatureFlagKeys.FlexibleCollections);
         // Arrange
         var model = new CollectionBulkDeleteRequestModel
         {
@@ -225,6 +236,7 @@ public class CollectionsControllerTests
     [Theory, BitAutoData]
     public async Task PostBulkCollectionAccess_Success(User actingUser, ICollection<Collection> collections, SutProvider<CollectionsController> sutProvider)
     {
+        sutProvider.EnableFeatureFlag(FeatureFlagKeys.FlexibleCollections);
         // Arrange
         var userId = Guid.NewGuid();
         var groupId = Guid.NewGuid();
@@ -271,6 +283,7 @@ public class CollectionsControllerTests
     [Theory, BitAutoData]
     public async Task PostBulkCollectionAccess_CollectionsNotFound_Throws(User actingUser, ICollection<Collection> collections, SutProvider<CollectionsController> sutProvider)
     {
+        sutProvider.EnableFeatureFlag(FeatureFlagKeys.FlexibleCollections);
         var userId = Guid.NewGuid();
         var groupId = Guid.NewGuid();
         var model = new BulkCollectionAccessRequestModel
@@ -302,6 +315,7 @@ public class CollectionsControllerTests
     [Theory, BitAutoData]
     public async Task PostBulkCollectionAccess_AccessDenied_Throws(User actingUser, ICollection<Collection> collections, SutProvider<CollectionsController> sutProvider)
     {
+        sutProvider.EnableFeatureFlag(FeatureFlagKeys.FlexibleCollections);
         var userId = Guid.NewGuid();
         var groupId = Guid.NewGuid();
         var model = new BulkCollectionAccessRequestModel
diff --git a/test/Api.Test/Controllers/LegacyCollectionsControllerTests.cs b/test/Api.Test/Controllers/LegacyCollectionsControllerTests.cs
new file mode 100644
index 0000000000..68683837d1
--- /dev/null
+++ b/test/Api.Test/Controllers/LegacyCollectionsControllerTests.cs
@@ -0,0 +1,254 @@
+using Bit.Api.Controllers;
+using Bit.Api.Models.Request;
+using Bit.Core.Context;
+using Bit.Core.Entities;
+using Bit.Core.Exceptions;
+using Bit.Core.Models.Data;
+using Bit.Core.OrganizationFeatures.OrganizationCollections.Interfaces;
+using Bit.Core.Repositories;
+using Bit.Core.Services;
+using Bit.Test.Common.AutoFixture;
+using Bit.Test.Common.AutoFixture.Attributes;
+using NSubstitute;
+using Xunit;
+
+namespace Bit.Api.Test.Controllers;
+
+/// <summary>
+/// CollectionsController tests that use pre-Flexible Collections logic. To be removed when the feature flag is removed.
+/// Note the feature flag defaults to OFF so it is not explicitly set in these tests.
+/// </summary>
+[ControllerCustomize(typeof(CollectionsController))]
+[SutProviderCustomize]
+public class LegacyCollectionsControllerTests
+{
+    [Theory, BitAutoData]
+    public async Task Post_Success(Guid orgId, SutProvider<CollectionsController> sutProvider)
+    {
+        sutProvider.GetDependency<ICurrentContext>()
+            .OrganizationManager(orgId)
+            .Returns(true);
+
+        sutProvider.GetDependency<ICurrentContext>()
+            .EditAnyCollection(orgId)
+            .Returns(false);
+
+        var collectionRequest = new CollectionRequestModel
+        {
+            Name = "encrypted_string",
+            ExternalId = "my_external_id"
+        };
+
+        _ = await sutProvider.Sut.Post(orgId, collectionRequest);
+
+        await sutProvider.GetDependency<ICollectionService>()
+            .Received(1)
+            .SaveAsync(Arg.Any<Collection>(), Arg.Any<IEnumerable<CollectionAccessSelection>>(), null);
+    }
+
+    [Theory, BitAutoData]
+    public async Task Put_Success(Guid orgId, Guid collectionId, Guid userId, CollectionRequestModel collectionRequest,
+        SutProvider<CollectionsController> sutProvider)
+    {
+        sutProvider.GetDependency<ICurrentContext>()
+            .ViewAssignedCollections(orgId)
+            .Returns(true);
+
+        sutProvider.GetDependency<ICurrentContext>()
+            .EditAssignedCollections(orgId)
+            .Returns(true);
+
+        sutProvider.GetDependency<ICurrentContext>()
+            .UserId
+            .Returns(userId);
+
+        sutProvider.GetDependency<ICollectionRepository>()
+            .GetByIdAsync(collectionId, userId)
+            .Returns(new CollectionDetails
+            {
+                OrganizationId = orgId,
+            });
+
+        _ = await sutProvider.Sut.Put(orgId, collectionId, collectionRequest);
+    }
+
+    [Theory, BitAutoData]
+    public async Task Put_CanNotEditAssignedCollection_ThrowsNotFound(Guid orgId, Guid collectionId, Guid userId, CollectionRequestModel collectionRequest,
+        SutProvider<CollectionsController> sutProvider)
+    {
+        sutProvider.GetDependency<ICurrentContext>()
+            .EditAssignedCollections(orgId)
+            .Returns(true);
+
+        sutProvider.GetDependency<ICurrentContext>()
+            .UserId
+            .Returns(userId);
+
+        sutProvider.GetDependency<ICollectionRepository>()
+            .GetByIdAsync(collectionId, userId)
+            .Returns(Task.FromResult<CollectionDetails>(null));
+
+        _ = await Assert.ThrowsAsync<NotFoundException>(async () => await sutProvider.Sut.Put(orgId, collectionId, collectionRequest));
+    }
+
+    [Theory, BitAutoData]
+    public async Task GetOrganizationCollectionsWithGroups_NoManagerPermissions_ThrowsNotFound(Organization organization, SutProvider<CollectionsController> sutProvider)
+    {
+        sutProvider.GetDependency<ICurrentContext>().ViewAssignedCollections(organization.Id).Returns(false);
+
+        await Assert.ThrowsAsync<NotFoundException>(() => sutProvider.Sut.GetManyWithDetails(organization.Id));
+        await sutProvider.GetDependency<ICollectionRepository>().DidNotReceiveWithAnyArgs().GetManyByOrganizationIdWithAccessAsync(default);
+        await sutProvider.GetDependency<ICollectionRepository>().DidNotReceiveWithAnyArgs().GetManyByUserIdWithAccessAsync(default, default);
+    }
+
+    [Theory, BitAutoData]
+    public async Task GetOrganizationCollectionsWithGroups_AdminPermissions_GetsAllCollections(Organization organization, User user, SutProvider<CollectionsController> sutProvider)
+    {
+        sutProvider.GetDependency<ICurrentContext>().UserId.Returns(user.Id);
+        sutProvider.GetDependency<ICurrentContext>().ViewAllCollections(organization.Id).Returns(true);
+        sutProvider.GetDependency<ICurrentContext>().OrganizationAdmin(organization.Id).Returns(true);
+
+        await sutProvider.Sut.GetManyWithDetails(organization.Id);
+
+        await sutProvider.GetDependency<ICollectionRepository>().Received().GetManyByOrganizationIdWithAccessAsync(organization.Id);
+        await sutProvider.GetDependency<ICollectionRepository>().Received().GetManyByUserIdWithAccessAsync(user.Id, organization.Id);
+    }
+
+    [Theory, BitAutoData]
+    public async Task GetOrganizationCollectionsWithGroups_MissingViewAllPermissions_GetsAssignedCollections(Organization organization, User user, SutProvider<CollectionsController> sutProvider)
+    {
+        sutProvider.GetDependency<ICurrentContext>().UserId.Returns(user.Id);
+        sutProvider.GetDependency<ICurrentContext>().ViewAssignedCollections(organization.Id).Returns(true);
+        sutProvider.GetDependency<ICurrentContext>().OrganizationManager(organization.Id).Returns(true);
+
+        await sutProvider.Sut.GetManyWithDetails(organization.Id);
+
+        await sutProvider.GetDependency<ICollectionRepository>().DidNotReceiveWithAnyArgs().GetManyByOrganizationIdWithAccessAsync(default);
+        await sutProvider.GetDependency<ICollectionRepository>().Received().GetManyByUserIdWithAccessAsync(user.Id, organization.Id);
+    }
+
+    [Theory, BitAutoData]
+    public async Task GetOrganizationCollectionsWithGroups_CustomUserWithManagerPermissions_GetsAssignedCollections(Organization organization, User user, SutProvider<CollectionsController> sutProvider)
+    {
+        sutProvider.GetDependency<ICurrentContext>().UserId.Returns(user.Id);
+        sutProvider.GetDependency<ICurrentContext>().ViewAssignedCollections(organization.Id).Returns(true);
+        sutProvider.GetDependency<ICurrentContext>().EditAssignedCollections(organization.Id).Returns(true);
+
+
+        await sutProvider.Sut.GetManyWithDetails(organization.Id);
+
+        await sutProvider.GetDependency<ICollectionRepository>().DidNotReceiveWithAnyArgs().GetManyByOrganizationIdWithAccessAsync(default);
+        await sutProvider.GetDependency<ICollectionRepository>().Received().GetManyByUserIdWithAccessAsync(user.Id, organization.Id);
+    }
+
+
+    [Theory, BitAutoData]
+    public async Task DeleteMany_Success(Guid orgId, User user, Collection collection1, Collection collection2, SutProvider<CollectionsController> sutProvider)
+    {
+        // Arrange
+        var model = new CollectionBulkDeleteRequestModel
+        {
+            Ids = new[] { collection1.Id, collection2.Id },
+        };
+
+        var collections = new List<Collection>
+            {
+                new CollectionDetails
+                {
+                    Id = collection1.Id,
+                    OrganizationId = orgId,
+                },
+                new CollectionDetails
+                {
+                    Id = collection2.Id,
+                    OrganizationId = orgId,
+                },
+            };
+
+        sutProvider.GetDependency<ICurrentContext>()
+            .DeleteAssignedCollections(orgId)
+            .Returns(true);
+
+        sutProvider.GetDependency<ICurrentContext>()
+            .UserId
+            .Returns(user.Id);
+
+        sutProvider.GetDependency<ICollectionService>()
+            .GetOrganizationCollectionsAsync(orgId)
+            .Returns(collections);
+
+        // Act
+        await sutProvider.Sut.DeleteMany(orgId, model);
+
+        // Assert
+        await sutProvider.GetDependency<IDeleteCollectionCommand>()
+            .Received(1)
+            .DeleteManyAsync(Arg.Is<IEnumerable<Collection>>(coll => coll.Select(c => c.Id).SequenceEqual(collections.Select(c => c.Id))));
+
+    }
+
+    [Theory, BitAutoData]
+    public async Task DeleteMany_CanNotDeleteAssignedCollection_ThrowsNotFound(Guid orgId, Collection collection1, Collection collection2, SutProvider<CollectionsController> sutProvider)
+    {
+        // Arrange
+        var model = new CollectionBulkDeleteRequestModel
+        {
+            Ids = new[] { collection1.Id, collection2.Id },
+        };
+
+        sutProvider.GetDependency<ICurrentContext>()
+            .DeleteAssignedCollections(orgId)
+            .Returns(false);
+
+        // Assert
+        await Assert.ThrowsAsync<NotFoundException>(() =>
+            sutProvider.Sut.DeleteMany(orgId, model));
+
+        await sutProvider.GetDependency<IDeleteCollectionCommand>()
+            .DidNotReceiveWithAnyArgs()
+            .DeleteManyAsync((IEnumerable<Collection>)default);
+
+    }
+
+
+    [Theory, BitAutoData]
+    public async Task DeleteMany_UserCanNotAccessCollections_FiltersOutInvalid(Guid orgId, User user, Collection collection1, Collection collection2, SutProvider<CollectionsController> sutProvider)
+    {
+        // Arrange
+        var model = new CollectionBulkDeleteRequestModel
+        {
+            Ids = new[] { collection1.Id, collection2.Id },
+        };
+
+        var collections = new List<Collection>
+            {
+                new CollectionDetails
+                {
+                    Id = collection2.Id,
+                    OrganizationId = orgId,
+                },
+            };
+
+        sutProvider.GetDependency<ICurrentContext>()
+            .DeleteAssignedCollections(orgId)
+            .Returns(true);
+
+        sutProvider.GetDependency<ICurrentContext>()
+            .UserId
+            .Returns(user.Id);
+
+        sutProvider.GetDependency<ICollectionService>()
+            .GetOrganizationCollectionsAsync(orgId)
+            .Returns(collections);
+
+        // Act
+        await sutProvider.Sut.DeleteMany(orgId, model);
+
+        // Assert
+        await sutProvider.GetDependency<IDeleteCollectionCommand>()
+            .Received(1)
+            .DeleteManyAsync(Arg.Is<IEnumerable<Collection>>(coll => coll.Select(c => c.Id).SequenceEqual(collections.Select(c => c.Id))));
+    }
+
+
+}