The Supreme Court ruled Monday that states can’t demand would-be voters prove they are citizens before casting ballots in federal elections.

The justices voted 7-2 to reject an Arizona law approved by voters in 2004 that requires residents to show “satisfactory evidence” of citizenship — such as naturalization papers, a birth certificate, passport or Indian tribal identification — before registering to vote. A standard Arizona driver’s license also is accepted because the state requires proof of citizenship to obtain one.

Defenders of the citizenship requirement said it’s a valuable tool to combat voter fraud. But the law’s critics argued it imposed an unfair burden on residents and threatens to disenfranchise minorities, the poor and others.

The 9th U.S. Circuit Court of Appeals — responding to a legal challenge by a group of Arizona residents, Indian tribes and civil-rights groups — had ruled the citizenship requirement conflicted with the 1993 federal law known as the “Motor Voter Law,” drafted in part to make it easier for people to register to vote. Arizona appealed, but the high court agreed with the lower court’s decision.

The courts in recent years have upheld several state laws that have strengthened rules requiring voters to show identification before casting ballots — most noteworthy a landmark 6-3 Supreme Court decision in 2008 that upheld a photo ID requirement in Indiana. Because the Arizona law centered around proof of citizenship — not just a photo ID — many legal analysts said the law presented justices with significantly different circumstances than other voting ID cases.