Hours after California voters approved a redistricting measure that would flip as many as five House seats for Democrats next year, California Republicans filed a lawsuit on Wednesday morning challenging the new maps.

The suit, filed in the U.S. District Court for the Central District of California, argues that the new maps are unconstitutional because they improperly use voters’ race as a factor in drawing districts and asks the court to block them from taking effect.

The lawsuit came the morning after California voters approved the redistricting measure, Proposition 50, which Gov. Gavin Newsom pushed to retaliate against gerrymandering that leaders in Texas and other Republican-led states approved at the request of President Trump.

It is not clear how successful the latest challenge will be. California Republicans were unsuccessful earlier this year at preventing the ballot measure through litigation, and Democrats have expressed confidence that their new maps will withstand legal scrutiny.

Proposition 50 suspended maps drawn by an independent commission and installed new congressional districts that were designed to help Democrats pick up five seats now held by Republicans. It was the most significant counterpunch by Democrats in a redistricting war that has swept the nation and upended political norms as Mr. Trump tries to keep the House of Representatives under Republican control.