MOUNTAIN VIEW, California: The U.S. Department of Justice is seeking the breakup of Google's digital advertising business, calling for the sale of its AdX marketplace and DFP ad-serving platform, following a federal judge's finding that the tech giant held illegal monopolies in two online ad-tech markets.

In a court filing late Monday, the DOJ said the proposed divestitures were essential to dismantling Alphabet's dominance and restoring competition in both the ad-exchange and publisher ad-server markets.

The request follows an April ruling by U.S. District Judge Leonie Brinkema in Alexandria, Virginia, who found that Google had "willfully acquired and maintained monopoly power" in these segments. A separate court previously ruled that Google also held an unlawful monopoly in online search.

Brinkema scheduled a trial for September to determine the appropriate remedies after hearing arguments from both sides.

Google, for its part, argued that it supports behavioral changes—such as opening real-time bidding to competitors—but opposes forced divestitures.

"The DOJ's additional proposals to force a divestiture of our ad tech tools go well beyond the Court's findings, have no basis in law, and would harm publishers and advertisers," said Lee-Anne Mulholland, Google's vice president of Regulatory Affairs, in a statement to Reuters.

Alphabet shares fell nearly 1.1 percent in premarket trading on Tuesday.

AdX serves as a marketplace where publishers auction unsold ad space in real-time, while DFP is used to manage and serve those ads. Together, the tools are essential for publishers and content providers to monetize digital inventory.

In 2023, Google had offered to sell AdX to settle a European Union antitrust investigation, but the offer was rejected by publishers who deemed the proposal insufficient.