diff --git a/encord_agents/fastapi/cors.py b/encord_agents/fastapi/cors.py
index 7e87ed04..4234484b 100644
--- a/encord_agents/fastapi/cors.py
+++ b/encord_agents/fastapi/cors.py
@@ -4,10 +4,16 @@
 interactions from the Encord platform.
 """
 
+import asyncio
+import json
 import typing
 from http import HTTPStatus
+from uuid import UUID
 
 from encord.exceptions import AuthorisationError
+from pydantic import ValidationError
+
+from encord_agents.core.data_model import FrameData
 
 try:
     from fastapi import FastAPI, Request
@@ -102,6 +108,45 @@ async def _authorization_error_exception_handler(request: Request, exc: Authoris
     )
 
 
+class FieldPairLockMiddleware(BaseHTTPMiddleware):
+    def __init__(
+        self,
+        app: ASGIApp,
+    ):
+        super().__init__(app)
+        self.field_locks: dict[tuple[UUID, UUID], asyncio.Lock] = {}
+        self.locks_lock = asyncio.Lock()
+
+    async def get_lock(self, frame_data: FrameData) -> asyncio.Lock:
+        lock_key = (frame_data.project_hash, frame_data.data_hash)
+        async with self.locks_lock:
+            if lock_key not in self.field_locks:
+                self.field_locks[lock_key] = asyncio.Lock()
+            return self.field_locks[lock_key]
+
+    async def dispatch(self, request: Request, call_next: RequestResponseEndpoint) -> Response:
+        if request.method != "POST":
+            return await call_next(request)
+        try:
+            body = await request.body()
+            try:
+                frame_data = FrameData.model_validate_json(body)
+            except ValidationError:
+                # Hope that route doesn't use FrameData
+                return await call_next(request)
+            lock = await self.get_lock(frame_data)
+            async with lock:
+                # Create a new request with the same body since we've already consumed it
+                request._body = body
+                return await call_next(request)
+        except Exception as e:
+            return Response(
+                content=json.dumps({"detail": f"Error in middleware: {str(e)}"}),
+                status_code=500,
+                media_type="application/json",
+            )
+
+
 def get_encord_app(*, custom_cors_regex: str | None = None) -> FastAPI:
     """
     Get a FastAPI app with the Encord middleware.
@@ -114,10 +159,12 @@ def get_encord_app(*, custom_cors_regex: str | None = None) -> FastAPI:
         FastAPI: A FastAPI app with the Encord middleware.
     """
     app = FastAPI()
+
     app.add_middleware(
         EncordCORSMiddleware,
         allow_origin_regex=custom_cors_regex or ENCORD_DOMAIN_REGEX,
     )
     app.add_middleware(EncordTestHeaderMiddleware)
+    app.add_middleware(FieldPairLockMiddleware)
     app.exception_handlers[AuthorisationError] = _authorization_error_exception_handler
     return app
diff --git a/tests/integration_tests/fastapi/test_dependencies.py b/tests/integration_tests/fastapi/test_dependencies.py
index 5d72a5ab..f1d3ee40 100644
--- a/tests/integration_tests/fastapi/test_dependencies.py
+++ b/tests/integration_tests/fastapi/test_dependencies.py
@@ -1,3 +1,4 @@
+import asyncio
 from http import HTTPStatus
 from typing import Annotated, NamedTuple
 from uuid import uuid4
@@ -306,3 +307,47 @@ def post_client(client: Annotated[EncordUserClient, Depends(dep_client)]) -> Non
         resp = client.post("/client", headers={"Origin": "https://example.com"})
         assert resp.status_code == 200, resp.content
         assert "Access-Control-Allow-Origin" not in resp.headers
+
+
+class TestFieldPairLockMiddleware:
+    context: SharedResolutionContext
+    client: TestClient
+    list_holder: list[int | tuple[int, str]]
+
+    # Set the project and first label row for the class
+    @classmethod
+    @pytest.fixture(autouse=True)
+    def setup(cls, context: SharedResolutionContext) -> None:
+        cls.context = context
+        app = get_encord_app()
+        cls.list_holder = []
+
+        @app.post("/threadsafe-endpoint")
+        async def threadsafe_endpoint(frame_data: FrameData) -> None:
+            cls.list_holder.append(frame_data.frame)
+            await asyncio.sleep(0.1)
+            cls.list_holder.append((frame_data.frame, "DONE"))
+
+        cls.client = TestClient(app)
+
+    def test_field_pair_lock_middleware(self) -> None:
+        assert self.list_holder == []
+        resp = self.client.post(
+            "/threadsafe-endpoint",
+            json={
+                "projectHash": self.context.project.project_hash,
+                "dataHash": self.context.video_label_row.data_hash,
+                "frame": 0,
+            },
+        )
+        assert resp.status_code == 200, resp.content
+        resp = self.client.post(
+            "/threadsafe-endpoint",
+            json={
+                "projectHash": self.context.project.project_hash,
+                "dataHash": self.context.video_label_row.data_hash,
+                "frame": 1,
+            },
+        )
+        assert resp.status_code == 200, resp.content
+        assert self.list_holder == [0, (0, "DONE"), 1, (1, "DONE")]