The U.S. Justice Department has filed a statement of interest in the NAACP lawsuit challenging elections boards in three North Carolina counties where voters complain they were inaccurately purged from voter rolls.

The NAACP went to federal court in Winston-Salem on Wednesday seeking intervention from U.S. District Judge Loretta Biggs.

In their lawsuit filed Monday, the NAACP and voters from Beaufort, Moore and Cumberland counties contend that local elections boards were violating federal law that prohibits voter roll purges within 95 days before an election.

In North Carolina, which has been a pivotal battleground state in the national elections, state law allows any registered voter to challenge another voter’s registration.

Challenges in Beaufort, Moore and Cumberland counties were done with the help of the Voter Integrity Project, a conservative-leaning organization that contends voter fraud is a problem, though very few cases have been prosecuted or proven either nationally or locally. Some of the challenges were based on the fact that campaign mailings sent to voters at a particular address were returned unopened.

“As described, the purge program at issue here rested on a mass mailing and the silence of voters largely unaware of the potential injury to their voting rights,” the U.S. Justice Department said in its statement of interest in the case. “A perfunctory administrative proceeding to consider evidence produced by a mass mailing does not turn an otherwise prohibited systematic process into an ‘individualized’ removal.”

Though some eligible voters, including a 100-year-old African-American woman from Belhaven, learned their registrations had been challenged, the NAACP and those who successfully overturned the challenges worry that more trouble awaits them at the polls.

The Rev. William J. Barber II, head of the state NAACP, has described the purging efforts as attempts to suppress the African-American vote, which often aligns with Democrats.

Jay Delancy, head of the Voter Integrity Project, has said the requests to purge the voter rolls were done, in part, to highlight a concern of his that North Carolina voting rolls are not purged as often as he would like of voters who have died or moved elsewhere.