The Obama administration’s challenge to a strict Alabama immigration law escalated when the U.S. Department of Justice requested a federal appeals court to block the law from going into effect.

The Justice Department’s bid for an injunction on a law it says steps on federal authority over immigration follows a judge’s ruling that upheld the harshest provisions.

Lawyers in the Justice Department asked the appeals court to hear its argument quickly, as Hispanic immigrants and families are reportedly fleeing Alabama or taking their children out of school.