Seeking to ensure Americans don’t have to pay more for their Coronas and Buds, the Justice Department filed a lawsuit Thursday to block a merger between two beer industry giants.

The agency’s lawsuit, filed in the U.S. District Court for the District of Columbia, challenges Anheuser-Busch InBev’s (ABI) acquisition of Grupo Modelo. The $20.1 billion deal could cost drinkers billions of dollars because it would lessen competition between the two companies, said Bill Baer, assistant attorney general in charge of the agency’s Antitrust Division.

We believe the acquisition is a bad deal for American consumers,” Baer told reporters during a conference call Thursday.

Baer said even an incremental increase in the costs of popular beers could have a significant impact on a marketplace that saw $80 billion in sales last year. Modelo has typically sought to compete by keeping its products, including the popular Corona, at lower price points. That has kept Anheuser-Busch and Miller from pushing their prices higher, the government contends.