Senior citizens and others would be harmed by the planned mergers of Anthem and Cigna as well as Aetna and Humana, the Department of Justice said Thursday in announcing an antitrust lawsuit to block the acquisitions.

“Two of the largest and fastest-growing providers of Medicare Advantage plans, which millions of seniors rely on for crucial medical coverage, would combine into just one,” Attorney General Loretta E. Lynch said at a press conference announcing the legal action, referring to Aetna and Humana.

The Anthem acquisition of Cigna is valued at $54 billion, and the Aetna acquisition of Humana is valued at $37 billion, according to the government.

“We all, including seniors, everyday workers and the previously uninsured and underinsured deserve affordable health insurance options,” Principal Deputy Associate Attorney General Bill Baer said. “Competition today drives these four successful firms to fight to give us affordable options. There is no reason to put that dynamic at risk, and that is why we are asking the court to stop these mergers and keep competition working for the benefit of the American consumer.”

Attorneys general from several states and the District of Columbia joined the Justice Department in the lawsuit, which alleges that the transactions would increase concentration and harm competition across the country, reducing from five to three the number of large, national health insurers in the country. In addition to price competition being limited, benefits would be reduced, incentives to provide wellness programs would be decreased and the quality of care would be lowered, they maintain.

Eleven states — California, Colorado, Connecticut, Georgia, Iowa, Maine, Maryland, New Hampshire, New York, Tennessee and Virginia — and the District of Columbia joined the department’s challenge of the Anthem – Cigna merger. Eight states — Delaware, Florida, Georgia, Iowa, Illinois, Ohio, Pennsylvania and Virginia — and the District of Columbia joined the department’s challenge of the Aetna – Humana merger.

Anthem, the country’s second-largest health insurer, is headquartered in Indianapolis. Aetna and Cigna, the third- and fourth-largest health insurance companies, respectively, are based in Hartford, CT. Humana, the fifth-largest insurer, is headquartered in Louisville, KY.