Google acted illegally to maintain a monopoly in some online advertising technology, a federal judge ruled on Thursday, adding to legal troubles that could reshape the $1.88 trillion company and alter its power over the internet.

Judge Leonie Brinkema of the U.S. District Court for the Eastern District of Virginia said in a 115-page ruling that Google had broken the law to build its dominance over the largely invisible system of technology that places advertisements on pages across the web. The Justice Department and a group of states had sued Google, arguing that its monopoly in ad technology allowed the company to charge higher prices and take a bigger portion of each sale.

“In addition to depriving rivals of the ability to compete, this exclusionary conduct substantially harmed Google’s publisher customers, the competitive process, and, ultimately, consumers of information on the open web,” said Judge Brinkema, who also dismissed one portion of the government’s case.

Google has increasingly faced a reckoning over the dominant role its products play in how people get information and conduct business online. Another federal judge ruled in August that the company had a monopoly in online search. He is now considering a request by the Justice Department to break the company up, with a three-week hearing on the matter scheduled to begin Monday.

Judge Brinkema, too, will have an opportunity to force changes to Google’s business. In its lawsuit, the Justice Department pre-emptively asked the court to force Google to sell some pieces of its ad technology business acquired over the years.

Together, the two rulings and their remedies could check Google’s influence and result in a sweeping overhaul of the company, which faces a potential major restructuring.

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