The Department of Justice is suing to block two major mergers that would consolidate the "Big Five" of the multitrillion-dollar health insurance industry to just three companies, Attorney General Loretta Lynch announced Thursday.

The DOJ seeks to block both Aetna's $37B bid for Humana and Anthem's $48B acquisition of Cigna. The mergers were announced in July 2015.

If the mergers went through, they'd "fundamentally reshape the health insurance industry," Lynch said at a DC press conference, raising costs and "drastically constricting competition in a number of key markets that tens of millions of Americans rely on."

The two mergers are "unprecedented in their size and scope," said principal deputy associate attorney general Bill Baer, the former head of the antitrust division. They could "increase insurance premiums, reduce benefits, lower the quality of healthcare, and slow innovation."

It's not just the federal government against the mergers: eight states plus DC are joining the suit against the Aetna-Humana tie-up, and nine states and DC join in opposing the Anthem-Cigna combo (which would form the country's largest health insurer by membership, with combined revenue measuring around $115B), Bloomberg reports. The companies intend to fight the lawsuits.