The Supreme Court on Thursday partly granted a request from the Republican National Committee to make Arizona enforce measures requiring people to show proof of U.S. citizenship when registering to vote.
In what is likely to be one of many election-related disputes to come before the court ahead of the November election, the justices allowed for one of three provisions of the state law to be enforced.
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The vote was 5-4 on allowing limited enforcement of the law with conservative justices in the majority. One conservative, Justice Amy Coney Barrett, joined the three liberal justices in dissent. The court, in a brief order, did not explain its reasoning.
Three conservative justices — Clarence Thomas, Samuel Alito and Neil Gorsuch — said they would have allowed all three provisions to be enforced.
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More than 40,000 people have registered to vote in federal elections in Arizona without providing proof of citizenship, although state officials say most are inactive voters, and only a small number will likely be affected. In the 2020 election, President Joe Biden beat former President Donald Trump in Arizona by just over 10,000 votes.
The provision the court allowed the state to enforce would require officials to turn away attempts to register to vote using the state's own registration form if the person has no documentary proof of citizenship.
But the court kept on hold separate provisions challenged by the Biden administration that would prevent people without proof of citizenship from voting in presidential elections or by mail if they registered to vote using a different, federal registration form.
"My concern is that changes to the process should not occur this close to an election. It creates confusion for voters," Arizona Secretary of State Adrian Fontes said in a statement.
The RNC hailed the decision as a win for election integrity, despite the lack of evidence that noncitizens vote in U.S. elections.
"While Democrats have worked to undermine basic election safeguards and make it easier for non-citizens to vote, we have fought tooth and nail to preserve citizenship requirements, see the law enforced, and secure our elections," RNC Chairman Michael Whatley said in a statement.
The Biden administration argued that the provisions the Supreme Court kept on hold violate a federal law called the National Voter Registration Act. That law requires those registering to vote in federal elections to attest that they are U.S. citizens but does not require documentary proof.
Arizona’s 2022 law, which has never been enforced, was itself a response to a 2013 Supreme Court ruling that invalidated an earlier attempt to impose a proof-of-citizenship requirement. Then, the Supreme Court said the National Voter Registration Act prevents states from adding additional requirements to forms people have to fill out to vote in federal elections.
In the ruling’s aftermath, Arizona enforced its proof-of-citizenship requirement for state elections, but not federal elections. This effectively created a tiered registration process, whereby certain prospective voters can register to vote in federal elections only.
While the Biden administration objected to the new provisions requiring proof of citizenship to vote for president or vote by mail, other plaintiffs, including voting rights groups, brought their own challenge focusing on the state registration form.
State officials, including Fontes, have declined to enforce the law. The law was passed by Republicans, but Fontes and other state leaders, including Attorney General Kris Mayes, are Democrats.
A federal judge ruled in favor of the plaintiffs, and the 9th U.S. Circuit Court of Appeals on Aug. 1 declined to block the ruling.
The RNC, joined by Republican leaders in the state legislature, said in court papers that the lower court ruling was “an unprecedented abrogation of the Arizona Legislature’s sovereign authority to determine the qualifications of voters and structure participation in its elections.”
Fontes had previously said that many of the more than 40,000 people who had registered to vote in federal elections only were likely students, service members and Native Americans who did not have birth certificates at hand when registering to vote. Only about 5,000 of the voters had registered to vote by mail.
Solicitor General Elizabeth Prelogar, representing the Biden administration, said in her court filing that “judicial intervention at this stage would undermine the orderly administration of the election, risking the disenfranchisement of thousands of voters who have already registered to vote.”
This story first appeared on NBCNews.com. More from NBC News: