A group of civil rights organizations sued Georgia on Thursday, accusing the state of violating federal voting rights law by requiring voters to register three months in advance of a federal runoff election. The lawsuit claims that the state’s policy will prevent “untold numbers of people from voting” in the state’s hotly contested runoff in June between Democrat Jon Ossoff and Republican Karen Handel in Georgia’s 6th Congressional District.

The National Voter Registration Act bars states from cutting off voter registration for federal elections—including runoff elections—more than 30 days before the election takes place. Yet under Georgia’s three-month deadline for runoff elections, those who didn’t register before March 22 will be barred from participation this summer. The lawsuit, filed by the Lawyers Committee for Civil Rights Under Law, Asian Americans Advancing Justice, and the Georgia chapter of the NAACP, is demanding the state allow voters to register until May 22.

“Citizens of Georgia are being unlawfully blocked from registering to vote,” Ezra Rosenberg, an attorney Lawyers’ Committee, said on a conference call with reporters Thursday. “We are taking up their cause to make sure people who want to vote can vote in the June 20th election.”

Francys Johnson, the president of the Georgia NAACP, said the policy is part of the state’s pattern “to make voting difficult, to make voting that something all Georgians cannot participate in.”

“We don’t expect Georgia to drop their longstanding practice of disenfranchising voters, so we have to go to court yet again,” he said. “We will fight them every step of the way, because this is a serious election with serious implications that go beyond Georgia.”

On Tuesday, fueled by donations from around the country and a groundswell of anti-Trump fervor, Ossoff came within a few points of flipping a seat held by Republicans since the Carter administration. Increasing turnout this summer, including registering new voters, could tip the balance in one of the country’s closest-watched races, triggered when Rep. Tom Price (R-GA) vacated the seat to run the Department of Health and Human Services.

As the plaintiffs seek an emergency injunction of the registration cutoff, the office of Georgia’s Secretary of State Brian Kemp (R) told the Atlanta Journal Constitution the lawsuit is a “completely political effort to attack Secretary Kemp” and promised, “We will fight it in court.”

Read the complaint: