diff --git a/.github/workflows/check-blocking-labels.yml b/.github/workflows/check-blocking-labels.yml
new file mode 100644
index 000000000..09f5c65b2
--- /dev/null
+++ b/.github/workflows/check-blocking-labels.yml
@@ -0,0 +1,46 @@
+# SPDX-FileCopyrightText: Contributors to the Power Grid Model project <powergridmodel@lfenergy.org>
+#
+# SPDX-License-Identifier: MPL-2.0
+
+
+name: Check Blocking Labels
+
+on:
+  # run pipeline on pull request
+  pull_request:
+    types:
+      - opened
+      - synchronize
+      - labeled
+      - unlabeled
+  # run pipeline on merge queue
+  merge_group:
+  # run this workflow manually from the Actions tab
+  workflow_dispatch:
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}-blocking-labels
+  cancel-in-progress: true
+
+jobs:
+  check-blocking-labels:
+    runs-on: ubuntu-latest
+    steps:
+
+      - name: do-not-merge
+        if: contains(github.event.pull_request.labels.*.name, 'do-not-merge')
+        run: |
+          echo "This pull request should not be merged (do-not-merge)"
+          exit 1
+
+      - name: merge-target-first
+        if: contains(github.event.pull_request.labels.*.name, 'merge-target-first')
+        run: |
+          echo "The target branch of this PR should be merged first (merge-target-first)"
+          exit 2
+
+      - name: needs-unit-tests
+        if: contains(github.event.pull_request.labels.*.name, 'needs-unit-tests')
+        run: |
+          echo "This pull request needs (more) unit tests before it may be merged (needs-unit-tests)"
+          exit 3
diff --git a/src/power_grid_model/validation/validation.py b/src/power_grid_model/validation/validation.py
index 10dba4a2e..6013294fd 100644
--- a/src/power_grid_model/validation/validation.py
+++ b/src/power_grid_model/validation/validation.py
@@ -978,6 +978,7 @@ def validate_regulator(data: SingleDataset, component: ComponentType) -> list[Va
 def validate_transformer_tap_regulator(data: SingleDataset) -> list[ValidationError]:
     errors = validate_regulator(data, ComponentType.transformer_tap_regulator)
     errors += _all_boolean(data, ComponentType.transformer_tap_regulator, "status")
+    errors += _all_unique(data, ComponentType.transformer_tap_regulator, "regulated_object")
     errors += _all_valid_enum_values(
         data, ComponentType.transformer_tap_regulator, "control_side", [BranchSide, Branch3Side]
     )
diff --git a/tests/unit/validation/test_input_validation.py b/tests/unit/validation/test_input_validation.py
index eab6d2ceb..8091a90ca 100644
--- a/tests/unit/validation/test_input_validation.py
+++ b/tests/unit/validation/test_input_validation.py
@@ -643,6 +643,7 @@ def test_validate_input_data_transformer_tap_regulator(input_data):
         UnsupportedTransformerRegulationError("transformer_tap_regulator", ["control_side", "regulated_object"], [54])
         in validation_errors
     )
+    assert NotUniqueError("transformer_tap_regulator", "regulated_object", [51, 54]) in validation_errors
 
 
 def test_fault(input_data):