The U.S. Department of Justice (DOJ) has asked a federal court to compel Google to divest key components of its advertising technology operations, arguing that such measures are necessary to restore competition in digital advertising markets.

The request follows a ruling last month by U.S. District Judge Leonie Brinkema, who found that Google had illegally maintained monopolies in the ad exchange and publisher ad server markets.

Specifically, the DOJ is seeking the separation of Google’s AdX platform—used to facilitate real-time ad auctions—and its DoubleClick for Publishers (DFP) ad server, which helps websites manage and deliver digital advertising.

In a filing made late on Monday, the DOJ said divestitures are the only viable solution to dismantle the Alphabet-owned company’s dominance and prevent future abuse of its market position. The case is set to go to trial in September, with further hearings scheduled to determine the scope and implementation of any potential remedies.

Google has pushed back against the proposal, arguing that behavioural remedies, such as opening up its ad tools to greater competition, should suffice. Lee-Anne Mulholland, Google’s vice president of Regulatory Affairs, said the DOJ’s divestiture demands “go well beyond the Court’s findings, have no basis in law, and would harm publishers and advertisers.”

Alphabet shares dipped by nearly 1.1% in premarket trading on Tuesday following the news.

This is the second major legal setback for Google in the U.S. after a separate court ruled last year that the company held an illegal monopoly in online search.