A US federal judge has ruled that Google must allow Android apps made by rival technology firms onto its Google Play app store for three years starting next month.
The change was among several remedies ordered by Judge James Donato in a case brought against Google by Epic Games, the maker of the hit video game Fortnite.
Google says it will appeal against the decision and ask for a pause to the proposed remedies.
In December, a jury sided with Epic, which says Google stifled competitors by controlling the distribution of apps and payments on Android phones.
In August, US District Judge Amit Mehta sided with the US Department of Justice, which accused the company of operating an illegal monopoly in online search.
Last month, District Judge Leonie Brinkema finished hearing arguments over similar government allegations that Google dominates the advertising technology market.
The company's critics say Google's fees of up to 30% on every payment made on its app store has meant higher prices for consumers.
"That is a rate they were able to charge because they were a monopoly," said Lee Hepner, Senior Legal Counsel at the American Economic Liberties Project.
Mr Hepner said that the ruling is likely change that.
"There's going to be a lot more incentive for developers to enter this market, and prices should be lower for consumers," he said.
The changes would put consumers’ privacy and security at risk, make it harder for developers to promote their apps, and reduce competition on devices," Google said in a statement.
Some legal experts have hailed the ruling as a meaningful challenge to the dominance of a handful of technology giants.
"It shows that courts are not necessarily opposed to asking dominant platforms to share access with rivals in the name of competition," said Rebecca Haw Allensworth, a professor at Vanderbilt Law School.
Among other remedies, the ruling called for Google to make its catalogue of apps available to competing app stores.
"That isn't something antitrust law would normally require," said Mark Lemley, professor at Stanford Law School. "But the judge correctly noted that once you have violated the antitrust laws, courts can order you to do affirmative things to undo the harm you caused, even though you didn't have the obligation to do those things in the first place."
Google had argued that its Play app store operates in a competitive landscape, citing competition with iPhone-maker Apple, which was also sued by Epic Games in 2020.
That case ended with an appeals court ruling that Apple does not have a monopoly in mobile games.
Monday's order is the latest legal blow suffered by Google in recent years on competition grounds.