NBCNEWS.COM - The Supreme Court on Monday struck down an Arizona law that requires people to submit proof of citizenship when they register to vote.
The vote was 7-2.
Several states said that such a law reduces voter fraud, but civil rights groups said it was an effort to discourage voting by legal immigrants. The case was argued and decided at a time when the country is considering how to change its immigration laws.
Citizenship is a requirement to vote in any federal election, and the federal registration form requires people to state, under penalty of perjury, that they are American citizens. States can use their own forms, but they must be equivalent to the federal form.
The Arizona law, known as Proposition 200, went further than the federal form by requiring applicants to provide proof of citizenship.
Challengers to the law argued that it put an extra burden on naturalized citizens. Using a naturalization document as proof would require an applicant to register in person, as opposed to through the mail, because federal law prohibits copying the document.
A federal appeals court said that Arizona had gone too far and essentially rejected the federal form. Arizona said it was not a rejection of the federal form any more than asking for ID at an airport is a rejection of a plane ticket.
Three other states — Alabama, Georgia and Kansas — have almost identical laws and joined Arizona in urging the court to uphold the additional requirements for proof of citizenship.
At an oral argument in March, Thomas Horne, a lawyer for Arizona, told the justices that the state was within its rights to ask for additional information beyond the simple federal form.
"It's extremely inadequate," Horne said. "It's essentially an honor system. It does not do the job."
"Well," answered Justice Sonia Sotomayor, "that's what the federal system decided was enough."
The court's conservatives appeared sympathetic to the Arizona side. Justice Antonin Scalia said that federal law clearly empowers the states to take additional action to assess a potential voter's eligibility.
"Under oath is not proof at all," he said. "It's just a statement."
Patricia Millett, a lawyer for groups opposed to the law, countered: "Statements under oath in a criminal case are proof beyond a reasonable doubt" in criminal cases that result in execution.
"It's a very serious oath," she said.
Arizona is known for its tough stance on immigration. Last year, the Supreme Court struck down some key provisions of a state law meant to crack down on illegal immigration.
But it let stand the most controversial part — a requirement that police making traffic stops check the immigration status of anyone they suspect of being in the country illegally.