Google abused its dominance to suppress competition in some digital advertising markets, a court has found in a ruling that could lead to the tech giant being forced to sell off parts of its business.

U.S. District Judge Leonie Brinkema concluded on Thursday that Google violated antitrust laws to build and illegally maintain a monopoly over the technology that places ads across the internet. For over a decade, the company imposed anticompetitive policies on customers and eliminated desirable features in ways that ultimately deprived rivals of the ability to compete, she said.

“This exclusionary conduct substantially harmed Google’s publisher customers, the competitive process, and, ultimately, consumers of information on the open web,” writes Brinkema.

The next step: Exploring the conditions that should be imposed on Google in light of the ruling. The government and a group of states argue that the Alphabet-owned company should be broken up,...