diff --git a/apis/kubefleet.dev/placement/v1alpha1/clusterclaim_types.go b/apis/kubefleet.dev/placement/v1alpha1/clusterclaim_types.go
index c9f3f9ab6..732e0aced 100644
--- a/apis/kubefleet.dev/placement/v1alpha1/clusterclaim_types.go
+++ b/apis/kubefleet.dev/placement/v1alpha1/clusterclaim_types.go
@@ -46,6 +46,7 @@ type ClusterClaim struct {
 	Status ClusterClaimStatus `json:"status,omitempty"`
 }
 
+// +kubebuilder:validation:XValidation:rule="has(self.clusterSelectorTerms) == has(oldSelf.clusterSelectorTerms)",message="the clusterSelectorTerms field cannot be added or removed after creation"
 type ClusterClaimSpec struct {
 	// The reference to the placement policy that adds the cluster claim.
 	//
diff --git a/config/crd/bases/placement.kubefleet.dev_clusterclaims.yaml b/config/crd/bases/placement.kubefleet.dev_clusterclaims.yaml
index 2bd4a6ad8..bb1fc81e0 100644
--- a/config/crd/bases/placement.kubefleet.dev_clusterclaims.yaml
+++ b/config/crd/bases/placement.kubefleet.dev_clusterclaims.yaml
@@ -220,6 +220,10 @@ spec:
             required:
             - placementPolicyRef
             type: object
+            x-kubernetes-validations:
+            - message: the clusterSelectorTerms field cannot be added or removed after
+                creation
+              rule: has(self.clusterSelectorTerms) == has(oldSelf.clusterSelectorTerms)
           status:
             description: The observed status of the cluster claim.
             properties:
diff --git a/test/apis/placement/v1beta1/clusterclaim_validation_integration_test.go b/test/apis/placement/v1beta1/clusterclaim_validation_integration_test.go
new file mode 100644
index 000000000..448198c67
--- /dev/null
+++ b/test/apis/placement/v1beta1/clusterclaim_validation_integration_test.go
@@ -0,0 +1,55 @@
+/*
+Copyright 2026 The KubeFleet Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package v1beta1
+
+import (
+	. "github.com/onsi/ginkgo/v2"
+	. "github.com/onsi/gomega"
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	"sigs.k8s.io/controller-runtime/pkg/client"
+
+	placementv1alpha1 "github.com/kubefleet-dev/kubefleet/apis/kubefleet.dev/placement/v1alpha1"
+)
+
+var _ = Describe("Test ClusterClaim API validation", func() {
+	It("should deny unsetting clusterSelectorTerms", func() {
+		clusterClaim := &placementv1alpha1.ClusterClaim{
+			ObjectMeta: metav1.ObjectMeta{
+				Name: "cluster-claim-selector-terms-immutability",
+			},
+			Spec: placementv1alpha1.ClusterClaimSpec{
+				PlacementPolicyRef: &placementv1alpha1.ObjectReference{
+					Name:       "test-placement-policy",
+					APIVersion: placementv1alpha1.GroupVersion.Version,
+					Kind:       "PlacementPolicy",
+				},
+				ClusterSelectorTerms: []placementv1alpha1.ClusterLabelAndPropertySelectorTerm{
+					{
+						MatchLabels: map[string]string{"region": "west"},
+					},
+				},
+			},
+		}
+		Expect(hubClient.Create(ctx, clusterClaim)).Should(Succeed())
+		DeferCleanup(func() {
+			Expect(client.IgnoreNotFound(hubClient.Delete(ctx, clusterClaim))).Should(Succeed())
+		})
+
+		clusterClaim.Spec.ClusterSelectorTerms = nil
+		Expect(hubClient.Update(ctx, clusterClaim)).Should(MatchError(ContainSubstring("the clusterSelectorTerms field cannot be added or removed after creation")))
+	})
+})
diff --git a/test/apis/placement/v1beta1/suite_test.go b/test/apis/placement/v1beta1/suite_test.go
index 58ff76bfa..5ea5cf06d 100644
--- a/test/apis/placement/v1beta1/suite_test.go
+++ b/test/apis/placement/v1beta1/suite_test.go
@@ -34,6 +34,7 @@ import (
 	"sigs.k8s.io/controller-runtime/pkg/envtest"
 	metricsserver "sigs.k8s.io/controller-runtime/pkg/metrics/server"
 
+	placementv1alpha1 "github.com/kubefleet-dev/kubefleet/apis/kubefleet.dev/placement/v1alpha1"
 	placementv1beta1 "github.com/kubefleet-dev/kubefleet/apis/placement/v1beta1"
 )
 
@@ -71,6 +72,7 @@ var _ = BeforeSuite(func() {
 	Expect(hubCfg).NotTo(BeNil())
 
 	Expect(placementv1beta1.AddToScheme(scheme.Scheme)).Should(Succeed())
+	Expect(placementv1alpha1.AddToScheme(scheme.Scheme)).Should(Succeed())
 
 	klog.InitFlags(flag.CommandLine)
 	flag.Parse()