WASHINGTON – The Supreme Court will struggle this week with the validity of an Arizona law that tries to keep illegal immigrants from voting by demanding all state residents show documents proving their U.S. citizenship before registering to vote in national elections.

The high court will hear arguments today over the legality of Arizona’s voter-approved requirement that prospective voters document their U.S. citizenship to use a registration form produced under the federal “Motor Voter” voter registration law that doesn’t require such documentation.

This case focuses on voter registration in Arizona, which has tangled frequently with the federal government over immigration issues involving the Mexican border. But it has broader implications because four other states – Alabama, Georgia, Kansas and Tennessee – have similar requirements, and 12 other states are contemplating similar legislation, officials say.