Brian Newby, executive director of the U.S. Election Assistance Commission (EAC), appears at a public meeting in Arlington, Va. in January. (Yorktel/U.S. Elections Assistance Commission via AP, File) (AP/AP)

A federal judge in Washington on Wednesday rejected a request that would have blocked Kansas, Alabama and Georgia from enforcing proof-of-citizenship requirements for people using a federal form to register to vote.

The decision by U.S. District Judge Richard J. Leon came in a lawsuit brought by the League of Women Voters, the NAACP in Georgia and other civil rights groups that sought a preliminary injunction.

The groups filed suit in February after Brian D. Newby, executive director of the U.S. Election Assistance Commission, notified the three states in a Jan. 29 letter that they could require documentary proof of citizenship on the federal voter registration form.

The Justice Department did not defend Newby’s decision and instead sided with the plaintiffs. A department spokeswoman declined to comment Wednesday.

Chris Carson, president of the League of Women Voters of the United States, said, “While we are disappointed in today’s decision, we will appeal to protect the critical rights of voters in these three states, especially during this election year.”

Kansas Secretary of State Kris Kobach discussed his state’s proof of citizenship requirements for voter registration in February in his office in Topeka, Ks. (Photo by Christopher Smith/ For the Washington Post) (Christopher Smith/For The Washington Post)

Kansas Secretary of State Kris W. Kobach, who defended the state measure in court, praised Leon’s decision as “exactly right,” saying that it was necessary to ensure that only U.S. citizens vote, a position “overwhelmingly supported by Kansas voters.”

Kansas implemented the requirement in 2013 for both its state registration form and a simpler federal version. Georgia and Alabama passed similar requirements in 2009 and 2011, but had not acted on the rules, plaintiffs said.

Before January, the federal commission had found such requirements invalid for the federal form, a position upheld by a U.S. appeals court in 2014.

Leon said the civil rights groups failed to establish that they would be “irreparably harmed” by the changes. He said the changes,“although an inconvenience,” in no way preclude “the organizational plaintiffs and their members from conducting their core activities of encouraging civic participation in both state and federal elections.”

“Injuries to voter registration drive efforts are far from certain in Alabama and Georgia where, on the record before me, the documentation of citizenship requirements are not even being enforced,” Leon added in a 25-page opinion.

In Kansas, Leon continued, “to the extent these inconveniences and added resources are injuries, they are not actually irreparable,” because the state said it will “retroactively register” individuals who seek to vote in federal elections but were barred solely because they failed to document their citizenship when they applied.