A divided Supreme Court on Thursday ruled that Arizona may require proof of citizenship when registering new voters for future elections.

But the court refused a GOP request to block voting in November by more than 40,000 people who had already registered without providing such proof.

The court did not explain its ruling, which arose from an emergency appeal filed by the Republican National Committee.

Conservative Justices Clarence Thomas, Samuel A. Alito Jr. and Neil M. Gorsuch said they would have granted the appeal in full.

Justices Elena Kagan, Sonia Sotomayor, Amy Coney Barrett and Ketanji Brown Jackson would have denied it entirely.

The justices usually frown on lawsuits or appeals that seek to change voting rules on the eve of an election.

In this instance, Arizona’s Republican leaders were seeking to enforce a new law that would forbid voting by Arizonans who do not show a birth certificate or passport when they register.

A federal judge in Phoenix had blocked the 2022 law from taking effect because it clashed with the federal “motor voter” law
and a 2013 Supreme Court ruling that had upheld the law in an Arizona case.

At that time, in a 7-2 decision, Justice Antonin Scalia said federal law required Arizona and other states to “accept and use” the standard federal form to register new voters even though it did not include a proof of citizenship.

In dissent then were Thomas and Alito.

Following that ruling, Arizona adopted a two-track system of voter registrations. Residents who registered to vote in state and local elections were required to show proof of their citizenship.

Those who registered through the federal form signed a sworn statement that they were U.S. citizens. These “federal only voters” were allowed to cast ballots only for members of Congress and the president.

The state later agreed in a 2018 consent decree to give full registration to new voters whose residence and citizenship could be confirmed through its motor vehicles department database.

But two years ago, the Republican-controlled Legislature passed a new law to prohibit registered voters who did not provide proof of their citizenship from casting ballots in a presidential election.

The Justice Department and voting rights advocates sued to challenge the law. Last year, U.S. District Judge Susan Bolton held a 10-day trial in Phoenix, and she blocked enforcement of the new proof-of-citizenship requirement.

The 9th Circuit Court of Appeals, by a 2-1 vote, refused to lift her order.

The RNC, the Arizona Senate and the speaker of the state assembly filed an emergency appeal with the Supreme Court on Aug. 8. They argued that the Arizona Legislature has the final authority to decide who can vote in the state’s elections.

But the Arizona attorney general and secretary of state, both Democrats, urged the court to turn down the appeal.

Adrian Fontes, the secretary of state, told the court a ruling upsetting the current registration rules would “create chaos and confusion.” He said newly registered voters who used the federal form would be disenfranchised, along with “the 42,301 federal only registrants” who will not be able to vote in the presidential election.