The justices ruled 7-2 Arizona's requirement of proof of citizenship before voter registration is pre-empted by federal law.
The Dallas Morning News, which praised the ruling editorially, said after the decision the high court was bucking a national trend.
The newspaper said a number of states have restricted early voting and voter registration drives, while in Florida, "the League of Women Voters was forced to suspend its voter registration efforts after 72 years because a new law greatly impedes its efforts."
The newspaper noted more than 30 states introduced such legislation in 2011 and the ID cards permitted vary widely.
But if last week's ruling, which affects federal elections only, translates to other challenges in other states, it would be a major blow to voter ID efforts. Seventeen states have enacted laws requiring the presentation of some type of government-issued photo identification, such as a driver's license, before voting. The Brennan Center for Justice at the New York University Law School said in federal voting those 17 states account for 218 of the 270 electoral votes needed to win the presidency.
Support for such laws usually breaks down by party. Republicans who have sponsored such laws say they are necessary to prevent widespread voter fraud. Democrats say Republicans have presented no evidence of widespread fraud, and the laws are only a thinly veiled campaign to suppress the votes of minorities, the elderly and the poor -- groups likely to vote Democratic.
In an unusual coalition at the Supreme Court, conservative Justice Antonin Scalia wrote the majority opinion, and was joined by Chief Justice John Roberts and the court's four liberals. Justice Anthony Kennedy wrote a separate opinion dissenting and joining in part, but concurring in the judgment.
The Arizona case pits the state requirement for proof of U.S. citizenship against the federal "Motor Voter" law that requires only filling out a form to register for federal elections. In 2004, Arizona voters adopted Proposition 200, a ballot initiative designed in part "to combat voter fraud by requiring voters to present proof of citizenship when they register to vote and to present identification when they vote on election day."
The case, Arizona vs. The Inter Tribal Council of Arizona Inc., first reached the U.S. Supreme Court in 2006's Purcell vs. Gonzalez. Though the justices did not reach a resolution, they sent the case back down to the lower courts.
A federal judge refused to issue an injunction against the implementation of the law in the case brought by a coalition of Hispanic, Indian and civil rights groups. However, a federal appellate panel, and then the entire 9th U.S. Circuit Court of Appeals in San Francisco reversed, saying the law violated Article I of the U.S. Constitution and the National Voter Registration Act, known as the "Motor Voter Act," which requires states to make it easier to register for federal elections. The act allows information gathered from license renewals, among other things, to be used for voter registration.
Article I, the election clause, says in part, the "times, places and manner of holding elections for senators and representatives, shall be prescribed in each state by the legislature thereof; but the Congress may at any time by law make or alter such regulations, except as to the places of choosing senators."
Arizona then successfully asked the U.S. Supreme Court for review.
In affirming the lower courts, Scalia said: "The National Voter Registration Act requires states to 'accept and use' a uniform federal form to register voters for federal elections. The ... federal form ... does not require documentary evidence of citizenship; rather, it requires only that an applicant aver, under penalty of perjury, that he is a citizen. Arizona law requires voter-registration officials to 'reject' any application for registration, including a federal form, ... not accompanied by concrete evidence of citizenship. The question is whether Arizona's evidence-of-citizenship requirement, as applied to federal form applicants, is pre-empted by the act's mandate that states accept and use' the federal form."
He added: "We conclude that the fairest reading of the statute is that a state-imposed requirement of evidence of citizenship not required by the federal form is 'inconsistent with' the NVRA's mandate that states "accept and use" the federal form. ... If this reading prevails, the [Constitution's] elections clause requires that Arizona's rule give way."
Voting rights advocates immediately claimed victory. But SCOTUSblog's veteran reporter Lyle Denniston, almost alone among commentators, had a word of caution.
Denniston said in an analysis the ruling "strengthened Congress' hand in expanding the ranks of eligible voters, and yet assured states that they retain the ultimate power to decide who gets to vote. The apparent bottom line: states cannot now require voters to show proof that they are U.S. citizens, but the court has given them a plan that could gain them that power."
Scalia acknowledged a state may have evidence beyond the federal form that might keep someone from voting.
"While the NVRA forbids states to demand that an applicant submit additional information beyond that required by the federal form, it does not preclude states from 'deny[ing] registration based on information in their possession establishing the applicant's ineligibility,'" Scalia said.
There was no immediate comment from Arizona's government on the ruling, but state Republican legislator John Kavanagh told The New York Times: "Arizona has a serious problem with illegal immigration, being one of the leading illegal entry states, so protecting the credibility of our election system requires that we exclude illegal aliens and any other non-citizen from voting. Not being able to request proof makes that impossible."
In Washington, Tom Fitton, president of the conservative Judicial Watch, issued a statement immediately after the ruling, saying: "The integrity of our nation's elections suffered a blow today from the Supreme Court. This issue takes on increasing urgency with the prospect of 11 million illegal immigrants being given amnesty. It is essential that our elections be secured by ensuring that only citizens register to vote."
The Mexican American Legal Defense and Educational Fund, which had filed suit against the Arizona law, to be joined later by other organizations, immediately issued a triumphant statement.
"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," said Nina Perales, MALDEF vice president of litigation and lead counsel for the voters who challenged Proposition 200. "The Supreme Court has affirmed that all U.S. citizens have the right to register to vote using the national postcard, regardless of the state in which they live."
MALDEF said in the two-year period following passage of Proposition 200, Arizona denied voter registration to more than 31,500 applicants for failing to provide additional documentation. In Maricopa County alone, which includes Phoenix and is under the jurisdiction of controversial Sheriff Joe Arpaio, community voter registration plunged by 44 percent, the group said.
MALDEF President and General Counsel Thomas A. Saenz said, "Arizona, and those states that choose to follow its irresponsible legislating, received a strong message today. The federal government has, through the NVRA, made clear that states may not place unnecessary and unreasonable obstacles to voter participation."
The Brennan Center for Justice in New York issued its own statement praising the ruling.
"Voters scored a huge victory today," Brennan Democracy Program Director Wendy Weiser said. "Congress recognized that voter registration must be made more accessible when it passed the National Voter Registration Act, and the court also affirmed that today. But more work remains to be done. In 2012, dozens of states passed laws making it harder to vote, and more voting restrictions have been introduced this year. The Supreme Court is still considering a challenge to the Voting Rights Act, one of our nation's key voting protections. These threats affect real people. We will continue to work with Congress and state legislators to further upgrade and modernize our voting system."
How important is the issue of voter ID and control of ballot access to the political parties in the United States? In 2000, Texas Gov. George W. Bush won Florida's electoral votes, and the presidency, by 537 votes.