A coalition of twelve U.S. states has filed an antitrust lawsuit seeking to stop Paramount’s proposed takeover of Warner Bros. Discovery, opening a major court battle over consolidation in the media and entertainment industry.

California Attorney General Rob Bonta said the merger would reduce competition, increase prices and lead to fewer films and television programs. The states asked a federal court in Northern California for a temporary restraining order and preliminary injunction that would prevent the transaction from closing while the case proceeds.

California was joined by Arizona, Colorado, Connecticut, Massachusetts, Minnesota, Nevada, New Jersey, New Mexico, New York, Oregon and Washington.

The lawsuit focuses on competition in wide-release film distribution, anticipated blockbuster films and cable-channel licensing. State officials allege that combining Paramount and Warner Bros. Discovery would reduce the variety, quality and volume of content while threatening consumers with higher prices.

Paramount said it would fight the case vigorously, calling the complaint wrong on both the facts and the law. The company argues that the combined business would strengthen competition against large streaming and technology platforms, including Netflix, and create more opportunities for creators and workers.

The U.S. Justice Department and regulators in several other markets have already approved the transaction. If the court grants an injunction, however, the deal could be delayed while the states pursue their claims.

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Video and reporting: CNN Business. Warner Bros. Discovery is CNN’s parent company. The complaint contains allegations that have not yet been decided by a court.