WASHINGTON — The Supreme Court agreed on Monday to decide whether Arizona may require proof of citizenship in order to register to vote in federal elections. The federal appeals court in San Francisco blocked the state law in April, saying it conflicted with a federal one.

The Supreme Court will hear arguments in the case early next year, and the law will remain suspended in the meantime.

The state law requires prospective voters to prove that they are citizens by providing copies of or information concerning various documents, including birth certificates, passports, naturalization papers or Arizona driver’s licenses, which are available only to people who are in the state lawfully.

The federal law, the National Voter Registration Act of 1993, allows voters to register using a federal form that asks, “Are you a citizen of the United States?” Prospective voters must check a box for yes or no, and they must sign the form, swearing that they are citizens under penalty of perjury.