The US Supreme Court has begun hearing a case which could bring about a profound change in American immigration policy.
Judges will decide whether Arizona has the right to pass its own state legislation to help deal with illegal migrants.
At present, immigration is the responsibility of the national government.
Campaigners say Arizona’s move is a violation of civil rights. Police can stop suspected illegal immigrants and demand proof of citizenship without probable cause.
But polls show more than half of Americans want the law upheld. The case comes as a separate report claims illegal migration from Mexico has come to a standstill and may have even reversed.
The court is due to rule in June.