Ahead of an emergency hearing on voter challenges, the U.S. Justice Department said several North Carolina counties apparently violated federal procedures for removing voters from the rolls based on undelivered mail.

The Justice Department court filing late Tuesday came ahead of arguments in court by the NAACP on Wednesday that at least three counties purged voter rolls through a process that disproportionately targets blacks.

Voters are being removed because of challenges filed by activists, which the NAACP says is illegal under federal law less than 90 days before an election. However, state officials say the process is legal under state law.

Justice Department lawyers said that if the NAACP allegations are true, they represent violations of the National Voting Rights Act.

The Justice Department writes that counties can’t remove voters “using only mail returned as undeliverable and without following specific required procedures,” nor can they carry out “systematic removals within 90 days of a Federal election.”

Early voting has already begun in North Carolina, a critical swing state that the NAACP has taken to court previously over issues such as voter identification.

The group’s lawsuit cites Cumberland, Moore and Beaufort counties, where activists have challenged thousands of voters’ names. The people filing challenges in Cumberland and Moore counties say they’re volunteers with the Voter Integrity Project, which says it wants to reduce the potential for voter fraud.

In most cases, mail sent to an address is returned as undeliverable, which county boards can accept as evidence that the voter no longer lives there.

The lawsuit says the state law, and the removals, are in violation of the National Voter Registration Act. It also asks to restore the names of voters who already have been removed. The emergency hearing Wednesday was taking place in U.S. District Court in Winston-Salem.

At least 4,500 voters have been challenged in Beaufort, Cumberland and Moore counties in August and September — with more than 3,900 of those in Cumberland County, the director of the State Board of Elections, Kim Westbrook Strach, said in a letter to the NAACP.

However, it’s not clear how many of those people have had their registrations struck from the rolls. Elections officials and the challengers say few people attend the hearings over their challenges; many have moved and haven’t updated their registration, while others have died.

(AP)