June 29 (UPI) -- The U.S. Supreme Court has agreed Monday to hear a case over Arizona's election law requiring documentary proof of citizenship in voting. The high court will hear arguments over whether federal law prohibits such a law when voting in state elections. The court will hear the case during its next term which starts in October. It is already illegal for non-U.S. citizens to vote in federal and state elections. Some municipalities allow noncitizen voting in local elections.