WASHINGTON — The Justice Department filed a lawsuit Thursday to stop Anheuser-Busch InBev’s proposed $20.1 billion purchase of Mexican brewer Grupo Modelo, which would unite the ownership of popular beers like Budweiser and Corona.

The government said the deal could lead to higher beer prices in this country because it would substantially reduce competition in the US beer market, particularly in 26 metropolitan areas. It said the merged firm would control nearly half the beer sales in the United States.