By Chantal Valery

The US Supreme Court on Monday invalidated a law that required people to show proof of nationality when registering to vote in the state of Arizona.

The law in the southwestern Republican-ruled state, put in place to keep undocumented immigrants from casting ballots, required documents that the federal government does not ask for when people complete a federal voter registration form.

Federal law “precludes Arizona from requiring a federal form applicant to submit information beyond that required by the form itself,” conservative Justice Antonin Scalia wrote on behalf of the panel’s majority.

This decision — backed by seven of the nine justices — only affects Arizona, which borders Mexico and often spars with Washington over immigration issues. But four other states — Alabama, Georgia, Kansas and Tennessee — have similar laws. Twelve additional states envisage doing the same.

The ruling is a victory for activists who saw it as a new infringement on the rights of minorities.

“The court has taken a vital step in ensuring the ballot remains free, fair, and accessible for all citizens,” said Laughlin McDonald of the American Civil Liberties Union.

In the United States, about 13 million people lack documentary proof of their citizenship, according to the group.

In Arizona alone, 90 percent of the more than 31,000 US citizens whose voter registration applications were denied were actually born in the United States, it added.

“Today’s decision is a victory for the federal government’s authority to regulate federal elections and protect the right to vote,” said Elizabeth Wydra of the Constitutional Accountability Center.

Nina Perales of MALDEF, a Latino civil rights organization, said “today’s decision sends a strong message that states cannot block their citizens from registering to vote by superimposing burdensome paperwork requirements on top of federal law.”

“The Supreme Court has affirmed that all US citizens have the right to register to vote using the national postcard, regardless of the state in which they live.”

The case was taken to the high court by Jesus Gonzalez, a naturalized American, whose registration was rejected under Arizona law.