In North Carolina, any person can revoke any other person’s voting rights without their knowledge. The process is simple: Someone sends a letter to thousands of people at once based on the address listed on their voter registration. He then gathers all mail returned as undeliverable, and sends another letter to those addresses, informing them that they are being removed from the voter rolls. If the voter does not appear at a county board of elections or return a notarized form, her voting rights are nullified. How easy is that?

Recently, Republicans in North Carolina have used this method to purge thousands of voters, most of them black Democrats, from the rolls. The NAACP has sued, alleging a violation of the National Voter Registration Act, whose procedural safeguards limit states’ ability to purge the voter rolls. Now the Justice Department has joined in, filing a statement of interest essentially pointing out that an egregious and unlawful voter suppression effort is currently underway in North Carolina.

The NVRA protects voting rights by ensuring that individuals have fair notice before getting removed from the voter rolls. Under the law, a jurisdiction can’t remove a voter from the rolls based solely on a change of address to a new jurisdiction without a lengthy notice and confirmation procedure. A jurisdiction is also barred from removing a voter from the rolls because she moved to a new address within the same jurisdiction. Finally, no jurisdiction can carry out a systematic voter purge within 90 days of a federal election.

Three North Carolina counties appear to have breached all of these rules by operating under state law, which is significantly laxer than the federal standards. Over the past few months, a group of Republicans have implemented a county-level voter-purge scheme targeting black Democrats. These vigilantes have gathered mail that was returned as undeliverable and challenged the voter registration of residents at those addresses. It isn’t entirely clear how these challengers managed to target primarily black voters, but they clearly have: In one recent purge, more than 65 percent of the purged voters were black, even though black people account for just 25.9 percent of the county’s population. Because the purges are occurring county by county, it’s unclear how many North Carolina voters have unknowingly had their voting rights nullified. But the NAACP alleges that at least 4,490 voters have been purged in three counties alone, and a majority of those people are minority Democrats.

On Wednesday, a federal court will consider the DOJ and NAACP’s claims. If it concludes that the voter purges run afoul of the NVRA, it will likely restore suffrage to the wrongly purged voters. (When state and federal law clash, as they do here, federal law wins.) That would certainly be a victory for voting rights. But to be effective, it would require the cooperation of county officials who so eagerly threw voters off the rolls in the first place. Thus far this election season, Republican officials have consistently ignored court orders pushing back against efforts to curb voting rights. It’s not clear that this case will be any different.

Read more Slate coverage of the election.