Kansas Secretary of State Kris Kobach discusses his state’s proof-of-citizenship voter registration requirementin his office in mid-February, 2015. (Christopher Smith for The Washington Post)

A U.S. elections agency must remove a proof-of-citizenship requirement from a mail-in federal voter registration form used for November’s election in Kansas, Alabama and Georgia, a federal appeals court panel in Washington ordered late Friday, reversing a lower court.

The 2-to-1 decision by the U.S. Court of Appeals for the District of Columbia Circuit came one day after civil rights groups in oral arguments said the provision could disenfranchise tens of thousands of U.S. citizens applying to vote in Kansas without required papers.

Kansas is the only state enforcing a demand to show documentation such as a birth certificate, passport or naturalization papers instead of accepting signed and sworn affirmation of citizenship to register to vote in federal races.

U.S. Appeals Court judges Judith W. Rogers and Stephen F. Williams granted a preliminary injunction while a lawsuit by the League of Women Voters and other groups against the document requirement is pending, saying the voter groups had shown “irreparable harm” caused by the change and were likely to prevail once the case is decided.

The court set aside a June 29 decision by U.S. District Judge Richard J. Leon that denied an injunction, and returned the case to him to decide. A hearing on the case is set for Monday.

The order was the latest victory for civil rights groups, Democratic lawyers and the Obama administration, who have asked federal appeals courts to knock down new voting laws passed in Texas, North Carolina and other states — part of their ongoing battle with conservative lawyers and Republican lawmakers over who will be eligible to vote in this year’s presidential contest.

In the current case, voter groups sued after what they called an unauthorized and unilateral decision Jan. 29 by Brian D. Newby, executive director of the U.S. Election Assistance Commission, to grant the three states’ requests to alter the federal registration form to incorporate state ID requirements.

U.S. Appeals Court Judge A. Raymond Randolph disagreed with his two colleagues Friday, quoting a 2013 Supreme Court decision that said it would “raise serious constitutional doubts” if the federal elections assistance body prevented a state from “enforcing its voter qualifications.”

The judges in the majority said the full assistance commission could vote to approve the states’ request for required citizenship documents if it desired, or else the states could sue in federal court if the commission denied the states’ request or failed to act on them.

Kansas Secretary of State Kris W. Kobach, who defended the requirements in court, did not immediately respond to a request for comment about the state’s next steps. At Thursday’s hearing, Kobach said any harm to potential voters was speculative, adding that if the state loses in court, it has said it will retroactively allow voters to cast ballots in federal races if their applications were canceled solely because they did not document citizenship.

Chris Carson, president of the League of Women Voters, said the group brought the suit because voting should be made easier, not harder. With just weeks to go before Election Day, Carson said, “We are grateful to the court of appeals for stopping this thinly veiled discrimination in its tracks. . . . All eligible Americans deserve the opportunity to register and vote without obstacles.”

“Hopefully this will put an end to shenanigans in the much-needed federal agency charged with helping to improve our elections,” said Wendy Weiser, director of the Democracy Program at the Brennan Center for Justice at New York University’s law school and a co-plaintiff with the Lawyers’ Committee for Civil Rights Under Law.