The U.S. Justice Department sued Alphabet Inc.’s Google in the most significant antitrust case against an American company in two decades, kicking off what promises to be a volley of legal actions against the search giant for allegedly abusing its market power.

Google, which controls about 90% of the online search market in the U.S., is the "unchallenged gateway” to the internet and is engaged in a variety of anticompetitive practices to maintain and extend its monopoly, the government said in a complaint filed Tuesday in Washington. The company has used exclusive deals costing billions of dollars to dominate search and lock out competition from rivals, the U.S. said.

"No one can feasibly challenge Google’s dominance in search and search advertising,” Attorney General William Barr said. "If we let Google continue its anticompetitive ways, we will lose the next wave of innovators and Americans may never get to benefit from the ‘next Google.’”