diff --git a/temporal-sdk/src/main/java/io/temporal/internal/client/WorkflowClientRequestFactory.java b/temporal-sdk/src/main/java/io/temporal/internal/client/WorkflowClientRequestFactory.java
index c8d9a3cca..f802283ef 100644
--- a/temporal-sdk/src/main/java/io/temporal/internal/client/WorkflowClientRequestFactory.java
+++ b/temporal-sdk/src/main/java/io/temporal/internal/client/WorkflowClientRequestFactory.java
@@ -210,6 +210,10 @@ SignalWithStartWorkflowExecutionRequest.Builder newSignalWithStartWorkflowExecut
       request.setVersioningOverride(startParameters.getVersioningOverride());
     }
 
+    if (startParameters.hasPriority()) {
+      request.setPriority(startParameters.getPriority());
+    }
+
     return request;
   }
 
diff --git a/temporal-sdk/src/test/java/io/temporal/internal/client/RootWorkflowClientInvokerPriorityPropagationTest.java b/temporal-sdk/src/test/java/io/temporal/internal/client/RootWorkflowClientInvokerPriorityPropagationTest.java
new file mode 100644
index 000000000..f6acf7e77
--- /dev/null
+++ b/temporal-sdk/src/test/java/io/temporal/internal/client/RootWorkflowClientInvokerPriorityPropagationTest.java
@@ -0,0 +1,86 @@
+package io.temporal.internal.client;
+
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.when;
+
+import io.temporal.api.common.v1.Priority;
+import io.temporal.api.workflowservice.v1.SignalWithStartWorkflowExecutionRequest;
+import io.temporal.api.workflowservice.v1.SignalWithStartWorkflowExecutionResponse;
+import io.temporal.client.WorkflowClientOptions;
+import io.temporal.client.WorkflowOptions;
+import io.temporal.common.interceptors.Header;
+import io.temporal.common.interceptors.WorkflowClientCallsInterceptor.WorkflowSignalWithStartInput;
+import io.temporal.common.interceptors.WorkflowClientCallsInterceptor.WorkflowStartInput;
+import io.temporal.internal.client.external.GenericWorkflowClient;
+import io.temporal.internal.common.ProtoConverters;
+import org.junit.Assert;
+import org.junit.Before;
+import org.junit.Test;
+import org.mockito.ArgumentCaptor;
+
+/**
+ * Unit test guarding that {@link RootWorkflowClientInvoker#signalWithStart} propagates the {@link
+ * io.temporal.common.Priority} set on {@link WorkflowOptions} onto the outgoing {@link
+ * SignalWithStartWorkflowExecutionRequest}. A plain {@code start} already carries priority, so this
+ * asserts the signalWithStart path stays in sync. Priority also carries the fairness fields, so a
+ * regression here silently drops fairness as well.
+ */
+public class RootWorkflowClientInvokerPriorityPropagationTest {
+
+  private static final String NAMESPACE = "test-namespace";
+  private static final String WORKFLOW_ID = "wf-target";
+
+  private GenericWorkflowClient genericClient;
+  private RootWorkflowClientInvoker invoker;
+
+  @Before
+  public void setUp() {
+    genericClient = mock(GenericWorkflowClient.class);
+    invoker =
+        new RootWorkflowClientInvoker(
+            genericClient,
+            WorkflowClientOptions.newBuilder()
+                .setNamespace(NAMESPACE)
+                .validateAndBuildWithDefaults(),
+            new WorkerFactoryRegistry());
+  }
+
+  @Test
+  public void signalWithStartPropagatesPriorityAndFairness() {
+    io.temporal.common.Priority priority =
+        io.temporal.common.Priority.newBuilder()
+            .setPriorityKey(5)
+            .setFairnessKey("tenant-123")
+            .setFairnessWeight(2.5f)
+            .build();
+    WorkflowOptions options =
+        WorkflowOptions.newBuilder().setTaskQueue("tq").setPriority(priority).build();
+
+    when(genericClient.signalWithStart(any(SignalWithStartWorkflowExecutionRequest.class)))
+        .thenReturn(
+            SignalWithStartWorkflowExecutionResponse.newBuilder().setRunId("target-run").build());
+
+    invoker.signalWithStart(newSignalWithStartInput(options));
+
+    ArgumentCaptor<SignalWithStartWorkflowExecutionRequest> captor =
+        ArgumentCaptor.forClass(SignalWithStartWorkflowExecutionRequest.class);
+    org.mockito.Mockito.verify(genericClient).signalWithStart(captor.capture());
+    SignalWithStartWorkflowExecutionRequest sent = captor.getValue();
+
+    Assert.assertTrue("request should carry priority", sent.hasPriority());
+    Priority expected = ProtoConverters.toProto(priority);
+    Assert.assertEquals(expected, sent.getPriority());
+    Assert.assertEquals(5, sent.getPriority().getPriorityKey());
+    Assert.assertEquals("tenant-123", sent.getPriority().getFairnessKey());
+    Assert.assertEquals(2.5f, sent.getPriority().getFairnessWeight(), 0.0f);
+  }
+
+  private static WorkflowSignalWithStartInput newSignalWithStartInput(WorkflowOptions options) {
+    WorkflowStartInput startInput =
+        new WorkflowStartInput(
+            WORKFLOW_ID, "TestWorkflow", Header.empty(), new Object[] {}, options);
+    return new WorkflowSignalWithStartInput(
+        startInput, "test-signal", new Object[] {"signal-payload"});
+  }
+}