diff --git a/src/Controller/UserController.php b/src/Controller/UserController.php
index e86d7c2..819c664 100644
--- a/src/Controller/UserController.php
+++ b/src/Controller/UserController.php
@@ -872,6 +872,9 @@ class UserController extends AbstractController
                 $email = $user->getEmail();
                 $existingUser = $this->userRepository->findOneBy(['email' => $email]);
 
+                if($this->userService->checkUserOrganizationLinkExists($existingUser, $org)){
+                    return $this->json(['error' => "L'utilisateur existe déjà dans votre organisation"], 400);
+                }
                 // CASE A: User exists -> Add to org
                 if ($existingUser) {
                     // Check if already in org to avoid logic errors or duplicate logs
diff --git a/src/Service/UserService.php b/src/Service/UserService.php
index a40dc47..2c981e8 100644
--- a/src/Service/UserService.php
+++ b/src/Service/UserService.php
@@ -750,4 +750,21 @@ class UserService
         $this->entityManager->flush();
     }
 
+    /*
+     * Check if the user organization link doesn't already exist
+     * Return true if the link exists, false otherwise.
+     *
+     * @param User $user
+     * @param Organization $organization
+     * @return bool
+     * */
+    public function checkUserOrganizationLinkExists(User $user, Organizations $organization): bool
+    {
+        $existingLink = $this->entityManager->getRepository(UsersOrganizations::class)->findOneBy([
+            'users' => $user,
+            'organization' => $organization
+        ]);
+
+        return $existingLink !== null;
+    }
 }