diff --git a/ironic/api/controllers/v1/portgroup.py b/ironic/api/controllers/v1/portgroup.py
index 732d55600c..916ddee96a 100644
--- a/ironic/api/controllers/v1/portgroup.py
+++ b/ironic/api/controllers/v1/portgroup.py
@@ -188,6 +188,7 @@ class Portgroup(base.APIBase):
 class PortgroupPatchType(types.JsonPatchType):
 
     _api_base = Portgroup
+    _extra_non_removable_attrs = {'/mode'}
 
     @staticmethod
     def internal_attrs():
diff --git a/ironic/tests/unit/api/v1/test_portgroups.py b/ironic/tests/unit/api/v1/test_portgroups.py
index 1e4b1dc2f3..b80a002297 100644
--- a/ironic/tests/unit/api/v1/test_portgroups.py
+++ b/ironic/tests/unit/api/v1/test_portgroups.py
@@ -852,10 +852,21 @@ class TestPatch(test_api_base.BaseApiTest):
 
     def test_update_portgroup_mode_properties_bad_api_version(self, mock_upd):
         self._test_update_portgroup_mode_properties_bad_api_version(
-            [{'path': '/mode', 'op': 'remove'}], mock_upd)
+            [{'path': '/mode', 'op': 'add', 'value': '802.3ad'}], mock_upd)
         self._test_update_portgroup_mode_properties_bad_api_version(
             [{'path': '/properties/abc', 'op': 'add', 'value': 123}], mock_upd)
 
+    def test_remove_mode_not_allowed(self, mock_upd):
+        response = self.patch_json('/portgroups/%s' % self.portgroup.uuid,
+                                   [{'path': '/mode',
+                                     'op': 'remove'}],
+                                   expect_errors=True,
+                                   headers=self.headers)
+        self.assertEqual(http_client.BAD_REQUEST, response.status_int)
+        self.assertEqual('application/json', response.content_type)
+        self.assertTrue(response.json['error_message'])
+        self.assertFalse(mock_upd.called)
+
 
 class TestPost(test_api_base.BaseApiTest):
     headers = {api_base.Version.string: str(api_v1.MAX_VER)}
diff --git a/releasenotes/notes/add-portgroup-config-fields-cd21e35e9c210733.yaml b/releasenotes/notes/add-portgroup-config-fields-cd21e35e9c210733.yaml
index 48815f92d1..578b114d99 100644
--- a/releasenotes/notes/add-portgroup-config-fields-cd21e35e9c210733.yaml
+++ b/releasenotes/notes/add-portgroup-config-fields-cd21e35e9c210733.yaml
@@ -1,8 +1,9 @@
 ---
 features:
   - Adds ``mode`` and ``properties`` fields in the portgroup object. Both of
-    them are optional and can be set from the API. They are available starting
-    with API microversion 1.26. If the ``mode`` field of a portgroup is not
+    them are optional and can be set from the API, though it is forbidden to
+    remove the ``mode`` from the portgroup. They are available starting with
+    API microversion 1.26. If the ``mode`` field of a portgroup is not
     specified in a POST request, its value will be set to the value of the
     configuration option ``[DEFAULT]default_portgroup_mode``. The configuration
     option ``[DEFAULT]default_portgroup_mode`` has a value of ``active-backup``