diff --git a/backend/app/services/user.py b/backend/app/services/user.py
index 6550463..1b44d17 100644
--- a/backend/app/services/user.py
+++ b/backend/app/services/user.py
@@ -148,6 +148,8 @@ async def get_or_link_user(db: Session, sub: str, access_token: str) -> User:
 
     user = user_repo.get_by_auth0_sub(db, sub)
     if user is not None:
+        if not user.active:
+            raise LookupError(f"User account for {user.email} is deactivated. Contact an admin.")
         return user
 
     # First login: look up email from Auth0 userinfo
@@ -163,8 +165,8 @@ async def get_or_link_user(db: Session, sub: str, access_token: str) -> User:
         raise ValueError("Could not retrieve email from Auth0 userinfo")
 
     user = user_repo.get_by_email(db, email)
-    if user is None:
-        raise LookupError(f"No user record found for {email}. Contact an admin.")
+    if user is None or not user.active:
+        raise LookupError(f"No active user record found for {email}. Contact an admin.")
 
     user_repo.set_auth0_sub(db, user, sub)
     return user
diff --git a/backend/tests/test_auth.py b/backend/tests/test_auth.py
index 9539f45..9a9486a 100644
--- a/backend/tests/test_auth.py
+++ b/backend/tests/test_auth.py
@@ -1,10 +1,14 @@
 """Tests for Auth0 authentication middleware."""
 
+from unittest.mock import AsyncMock, MagicMock, patch
+
 import pytest
 from fastapi.testclient import TestClient
 
 from app.core.database import Base, get_db
 from app.main import app
+from app.models.user import User
+from app.services.user import get_or_link_user
 from tests.conftest import TestingSessionLocal, engine
 
 
@@ -77,3 +81,86 @@ def test_get_current_user_returns_claims(client):
     response = client.get("/courses")
     assert response.status_code != 401
     assert response.status_code != 403
+
+
+# ---------------------------------------------------------------------------
+# get_or_link_user: inactive users are blocked
+# ---------------------------------------------------------------------------
+
+
+def _mock_userinfo(email: str):
+    """Build a patch for httpx.AsyncClient returning the given email from /userinfo."""
+    resp = MagicMock()
+    resp.raise_for_status = MagicMock()
+    resp.json = MagicMock(return_value={"email": email})
+
+    client_mock = MagicMock()
+    client_mock.__aenter__ = AsyncMock(return_value=client_mock)
+    client_mock.__aexit__ = AsyncMock(return_value=None)
+    client_mock.get = AsyncMock(return_value=resp)
+
+    return patch("httpx.AsyncClient", return_value=client_mock)
+
+
+async def test_get_or_link_user_blocks_inactive_user_on_first_login(db_session):
+    """First login by an inactive user should raise LookupError."""
+    db_session.add(
+        User(
+            nuid=12345,
+            first_name="Inactive",
+            last_name="User",
+            email="inactive@example.com",
+            role="VIEWER",
+            auth0_sub=None,
+            active=False,
+        )
+    )
+    db_session.commit()
+
+    with _mock_userinfo("inactive@example.com"):
+        with pytest.raises(LookupError):
+            await get_or_link_user(db_session, sub="auth0|new-sub", access_token="token")
+
+    refreshed = db_session.query(User).filter(User.email == "inactive@example.com").first()
+    assert refreshed.auth0_sub is None, "inactive user should not be linked"
+
+
+async def test_get_or_link_user_blocks_inactive_user_on_subsequent_request(db_session):
+    """A user whose auth0_sub is already linked but who is now inactive should be blocked."""
+    db_session.add(
+        User(
+            nuid=67890,
+            first_name="Deactivated",
+            last_name="User",
+            email="deactivated@example.com",
+            role="VIEWER",
+            auth0_sub="auth0|linked-sub",
+            active=False,
+        )
+    )
+    db_session.commit()
+
+    with pytest.raises(LookupError):
+        await get_or_link_user(db_session, sub="auth0|linked-sub", access_token="token")
+
+
+async def test_get_or_link_user_allows_active_user_on_first_login(db_session):
+    """First login by an active user should link the sub and return the user."""
+    db_session.add(
+        User(
+            nuid=11111,
+            first_name="Active",
+            last_name="User",
+            email="active@example.com",
+            role="VIEWER",
+            auth0_sub=None,
+            active=True,
+        )
+    )
+    db_session.commit()
+
+    with _mock_userinfo("active@example.com"):
+        user = await get_or_link_user(db_session, sub="auth0|fresh-sub", access_token="token")
+
+    assert user.email == "active@example.com"
+    assert user.auth0_sub == "auth0|fresh-sub"
diff --git a/frontend/src/App.tsx b/frontend/src/App.tsx
index 63d7eda..5dabb19 100644
--- a/frontend/src/App.tsx
+++ b/frontend/src/App.tsx
@@ -6,35 +6,65 @@ import Faculty from './pages/Faculty';
 import Courses from './pages/Courses';
 import Sidebar from './components/Sidebar';
 import LoginButton from './components/LoginButton';
+import AccessDenied from './components/AccessDenied';
 import { useAuthInterceptor } from './hooks/useAuthInterceptor';
-import { UserProvider } from './context/UserContext';
+import { UserProvider, useUser } from './context/UserContext';
 
-function App() {
-  const { isAuthenticated, isLoading, error } = useAuth0();
-  useAuthInterceptor();
+function LoadingScreen() {
+  return (
+    <div className="min-h-screen bg-gray-50 flex items-center justify-center">
+      <div className="flex flex-col items-center gap-3 text-gray-500">
+        <div className="w-8 h-8 border-4 border-burgundy-200 border-t-burgundy-600 rounded-full animate-spin" />
+        <span className="text-sm font-medium">Loading...</span>
+      </div>
+    </div>
+  );
+}
 
-  if (isLoading) {
-    return (
-      <div className="min-h-screen bg-gray-50 flex items-center justify-center">
-        <div className="flex flex-col items-center gap-3 text-gray-500">
-          <div className="w-8 h-8 border-4 border-burgundy-200 border-t-burgundy-600 rounded-full animate-spin" />
-          <span className="text-sm font-medium">Loading...</span>
-        </div>
+function ErrorScreen({ message }: { message: string }) {
+  return (
+    <div className="min-h-screen bg-gray-50 flex items-center justify-center">
+      <div className="bg-white rounded-2xl shadow-sm border border-red-100 p-8 max-w-sm w-full text-center">
+        <div className="text-3xl mb-2">⚠️</div>
+        <h2 className="text-lg font-semibold text-gray-900 mb-1">Something went wrong</h2>
+        <p className="text-sm text-gray-500">{message}</p>
       </div>
-    );
-  }
+    </div>
+  );
+}
+
+function AuthorizedApp() {
+  const { status, errorMessage } = useUser();
 
-  if (error) {
-    return (
-      <div className="min-h-screen bg-gray-50 flex items-center justify-center">
-        <div className="bg-white rounded-2xl shadow-sm border border-red-100 p-8 max-w-sm w-full text-center">
-          <div className="text-3xl mb-2">⚠️</div>
-          <h2 className="text-lg font-semibold text-gray-900 mb-1">Something went wrong</h2>
-          <p className="text-sm text-gray-500">{error.message}</p>
+  if (status === 'loading') return <LoadingScreen />;
+  if (status === 'blocked') return <AccessDenied />;
+  if (status === 'error') return <ErrorScreen message={errorMessage ?? 'Could not load your user profile.'} />;
+
+  return (
+    <div className="flex h-screen overflow-hidden bg-gray-50">
+      <Sidebar />
+      <main className="flex-1 overflow-y-auto">
+        <div className="p-8">
+          <Routes>
+            <Route path="/" element={<Navigate to="/schedules" replace />} />
+            <Route path="/schedules" element={<ScheduleList />} />
+            <Route path="/schedules/:scheduleId" element={<Schedules />} />
+            <Route path="/faculty/schedules/:scheduleId" element={<Schedules readOnly />} />
+            <Route path="/faculty" element={<Faculty />} />
+            <Route path="/courses" element={<Courses />} />
+          </Routes>
         </div>
-      </div>
-    );
-  }
+      </main>
+    </div>
+  );
+}
+
+function App() {
+  const { isAuthenticated, isLoading, error } = useAuth0();
+  useAuthInterceptor();
+
+  if (isLoading) return <LoadingScreen />;
+  if (error) return <ErrorScreen message={error.message} />;
 
   return (
     <BrowserRouter>
@@ -58,21 +88,7 @@ function App() {
         </div>
       ) : (
         <UserProvider>
-          <div className="flex h-screen overflow-hidden bg-gray-50">
-            <Sidebar />
-            <main className="flex-1 overflow-y-auto">
-              <div className="p-8">
-                <Routes>
-                  <Route path="/" element={<Navigate to="/schedules" replace />} />
-                  <Route path="/schedules" element={<ScheduleList />} />
-                  <Route path="/schedules/:scheduleId" element={<Schedules />} />
-                  <Route path="/faculty/schedules/:scheduleId" element={<Schedules readOnly />} />
-                  <Route path="/faculty" element={<Faculty />} />
-                  <Route path="/courses" element={<Courses />} />
-                </Routes>
-              </div>
-            </main>
-          </div>
+          <AuthorizedApp />
         </UserProvider>
       )}
     </BrowserRouter>
diff --git a/frontend/src/components/AccessDenied.tsx b/frontend/src/components/AccessDenied.tsx
new file mode 100644
index 0000000..bef1f81
--- /dev/null
+++ b/frontend/src/components/AccessDenied.tsx
@@ -0,0 +1,46 @@
+import { useAuth0 } from '@auth0/auth0-react';
+
+const AccessDenied = () => {
+  const { user, logout } = useAuth0();
+
+  const handleLogout = () => {
+    logout({ logoutParams: { returnTo: window.location.origin } });
+  };
+
+  return (
+    <div className="min-h-screen bg-gradient-to-br from-burgundy-50 via-white to-slate-50 flex items-center justify-center px-4">
+      <div className="w-full max-w-md">
+        <div className="text-center mb-8">
+          <img
+            src="/acs-logo.png"
+            alt="ACS Automated Course Scheduler"
+            className="h-16 w-auto max-w-full mx-auto mb-4 object-contain drop-shadow-sm"
+          />
+          <h1 className="text-3xl font-bold text-gray-900 tracking-tight">Access denied</h1>
+        </div>
+        <div className="bg-white rounded-2xl shadow-sm border border-gray-100 p-8">
+          <p className="text-gray-700 text-sm text-center mb-2">
+            {user?.email ? (
+              <>
+                <span className="font-medium text-gray-900">{user.email}</span> is not authorized to use this application.
+              </>
+            ) : (
+              'Your account is not authorized to use this application.'
+            )}
+          </p>
+          <p className="text-gray-500 text-sm text-center mb-6">
+            Contact an administrator if you believe this is a mistake.
+          </p>
+          <button
+            onClick={handleLogout}
+            className="w-full bg-burgundy-600 hover:bg-burgundy-700 active:bg-burgundy-800 text-white font-semibold py-2.5 px-4 rounded-xl transition-colors duration-150 shadow-sm"
+          >
+            Log out
+          </button>
+        </div>
+      </div>
+    </div>
+  );
+};
+
+export default AccessDenied;
diff --git a/frontend/src/context/UserContext.tsx b/frontend/src/context/UserContext.tsx
index 62e3451..7fe57e6 100644
--- a/frontend/src/context/UserContext.tsx
+++ b/frontend/src/context/UserContext.tsx
@@ -2,37 +2,61 @@ import { createContext, useContext, useEffect, useState } from 'react';
 import { useAuth0 } from '@auth0/auth0-react';
 import { getAutomatedCourseSchedulerAPI, type UserResponse } from '../api/generated';
 
+export type UserStatus = 'loading' | 'authorized' | 'blocked' | 'error';
+
 interface UserContextValue {
   me: UserResponse | null;
+  status: UserStatus;
+  errorMessage: string | null;
   meError: string | null;
   meLoading: boolean;
 }
 
-const UserContext = createContext<UserContextValue>({ me: null, meError: null, meLoading: true });
+const UserContext = createContext<UserContextValue>({
+  me: null,
+  status: 'loading',
+  errorMessage: null,
+  meError: null,
+  meLoading: true,
+});
 
 export function UserProvider({ children }: { children: React.ReactNode }) {
   const { isAuthenticated } = useAuth0();
   const [me, setMe] = useState<UserResponse | null>(null);
-  const [meError, setMeError] = useState<string | null>(null);
-  const [meLoading, setMeLoading] = useState(true);
+  const [status, setStatus] = useState<UserStatus>('loading');
+  const [errorMessage, setErrorMessage] = useState<string | null>(null);
 
   useEffect(() => {
     if (!isAuthenticated) return;
     getAutomatedCourseSchedulerAPI()
       .getMeApiUsersMeGet()
-      .then(setMe)
-      .catch((err: unknown) => {
-        const status = (err as { response?: { status?: number } })?.response?.status;
-        setMeError(
-          status === 403
-            ? 'Your Auth0 account is not linked to a DB user yet. Ask an admin to invite you or run bootstrap_admin.py.'
-            : 'Could not load your user profile.',
-        );
+      .then((user) => {
+        setMe(user);
+        setStatus('authorized');
       })
-      .finally(() => setMeLoading(false));
+      .catch((err: unknown) => {
+        const httpStatus = (err as { response?: { status?: number } })?.response?.status;
+        if (httpStatus === 403) {
+          setStatus('blocked');
+          setErrorMessage(null);
+        } else {
+          setStatus('error');
+          setErrorMessage('Could not load your user profile.');
+        }
+      });
   }, [isAuthenticated]);
 
-  return <UserContext.Provider value={{ me, meError, meLoading }}>{children}</UserContext.Provider>;
+  const value: UserContextValue = {
+    me,
+    status,
+    errorMessage,
+    meError: status === 'blocked'
+      ? 'Your account is not authorized to use this application.'
+      : errorMessage,
+    meLoading: status === 'loading',
+  };
+
+  return <UserContext.Provider value={value}>{children}</UserContext.Provider>;
 }
 
 export function useUser() {