A federal judge ruled in favor of the Justice Department in a civil antitrust lawsuit to block health insurer Anthem, Inc.’s acquisition of Cigna Corp.

Anthem, which is headquartered in Indianapolis but manages its California operations out of Thousand Oaks, offered to pay $54 billion for Cigna, a smaller insurer in Bloomfield, Conn. But U.S. District Judge Amy Berman Jackson in Washington, D.C. ruled for a coalition of the Justice Department and 11 states, including California.

“This merger would have stifled competition, harming consumers by increasing health insurance prices and slowing innovation aimed at lowering the costs of health care,” Acting Assistant Attorney General Brent Snyder said in a statement. “In concluding that Anthem’s acquisition of Cigna would violate federal antitrust laws, the court has protected consumers and the competition on which they rely.”

The district court’s opinion is temporarily under seal to allow the parties to review for confidentiality, according to the Justice Department.