The Supreme Court on Monday threw out an Arizona law that required people to prove they were citizens before they could use a new federal registration system meant to make signing up to vote easier.
In a 7-2 vote, the court ruled the Arizona law was trumped by the federal “motor voter” registration law.
The court's liberal wing sided with Scalia, as did Chief Justice John Roberts and Justice Anthony Kennedy.
In his majority opinion, Scalia wrote that Arizona was precluded “from requiring a federal form applicant to submit information beyond that required by the form itself.”
Thomas, writing the dissenting opinion, argued that the U.S. Constitution “authorizes states to determine the qualifications of voters in federal elections, which necessarily includes the related power to determine whether those qualifications are satisfied.”
The decision comes as a heated national debate over immigration intensifies in the Senate.
Supporters of a bipartisan immigration reform bill hope to move it out of the Senate by the end of the month with a strong vote. Republican opponents of the bill argue more provisions should be added to the bill to ensure the border is better secured.
The Supreme Court’s decision on Monday affirms a decision from the 9th U.S. Circuit Court of Appeals, which said that the National Voter Registration Act of 1993 supersedes the Arizona's Proposition 200, which was approved by the state’s voters in 1993.
The National Voter Act does not mandate that voters must prove citizenship in order to obtain registration forms to vote.
The liberal Constitutional Accountability Center (CAC) praised the high court's decision.
"At a time when states are engaged in voter suppression efforts, today’s opinion is an important reaffirmation that the text and history of the Elections Clause give the federal government broad power to preempt state law in order to protect the right to vote in federal elections," CAC Civil Rights Director David Gans said in a statement.
But Sen. Ted Cruz (R-Texas) criticized the ruling, saying it would increase voter fraud. He said he would file an amendment to the Senate immigration reform bill to counteract the high court's decision.
"This hole in federal statutory law allows non-citizens to register and thereby encourages voter fraud," Cruz wrote on his Facebook. "I will file a commonsense amendment to the immigration bill that permits states to require I.D. before registering voters."
Rep. Kyrsten Sinema (D-Ariz.) said she was “pleased” with the Supreme Court's ruling.
"Last November, as Arizona State University students lined up to vote, some were turned away or forced to cast 'provisional' votes because they had registered to vote via a federal voter registration form," Sinema said in a statement.
"Today’s Supreme Court decision, which requires Arizona elections officials to accept the federal registration form as a valid document, reaffirms our students' right to register and vote. “
Arizona has repeatedly faced legal challenges over laws related to citizenship and immigration. It is the state that passed a controversial law allowing law enforcement officials to arrest people they suspect are illegal immigrants.
The law struck down by the Supreme Court on Monday is similar to measures in Alabama, Georgia, Kansas and Tennessee. There are also 12 other states considering similar legislation, according to The Associated Press.
This story was updated at 2:42 p.m.