The Justice Department sued California on Thursday to block newly approved congressional boundaries, joining a fast-moving court battle that could help decide which party controls the U.S. House of Representatives after the 2026 midterm elections.

The complaint, filed in the U.S. District Court for the Central District of California, targets a new congressional map enacted through Proposition 50, a constitutional amendment California voters overwhelmingly approved last week. The ballot measure gave Democratic Gov. Gavin Newsom authority to overhaul district lines in response to a similar Republican effort in Texas backed by President Donald Trump.