Investing.com-- The U.S. Department of Justice (DOJ) on Monday called for a court-ordered breakup of Google parent Alphabet’s (NASDAQ: GOOGL ) online advertising empire, marking an escalation in its antitrust battle against the tech giant.

In a filing submitted Monday, the DOJ said Google should be forced to divest its advertising exchange AdX immediately, followed by a “phased” divestiture of its DoubleClick for Publishers (DFP) -- its publisher ad server -- two key components of its digital advertising stack.

The move follows U.S. District Judge Leonie Brinkema’s finding that Google monopolized the ad tech market, harming competition and innovation.

Google’s dominance in tools used to buy and sell online display ads has been under scrutiny, with the DOJ alleging that the company inflated costs for advertisers and reduced revenue for publishers.

Google has earlier denied wrongdoing and is expected to challenge any divestiture order.