The U.S. Supreme Court declined on Monday to halt key parts of a judge's order requiring Alphabet's Google to make major changes to its app store Play, as the company prepares to appeal a decision in a lawsuit brought by "Fortnite" maker Epic Games.

The justices turned down Google's request to temporarily freeze parts of the injunction won by Epic in its lawsuit accusing the tech giant of monopolising how consumers access apps on Android devices and pay for transactions within apps.

A federal appeals court in July upheld the judge’s sweeping order against Google.

The injunction issued last year by U.S. District Judge James Donato requires Google to allow users to download rival app stores within its Play store and make Play's app catalogue available to competitors. Those provisions do not take effect until July 2026.

The judge also said Google must allow developers to include external links in apps, enabling users to bypass Google's billing system. That part of the injunction is due to take effect later this month.

Donato issued his order in a lawsuit that Epic filed in 2020 against Google, alleging its restrictive app store rules violated antitrust law. Epic won a jury trial in San Francisco in 2023. Google has denied any wrongdoing.

Google has called Donato's order unprecedented, and said it would cause reputational harm, safety and security risks and put the company at a competitive disadvantage if allowed to take effect.

Google, in its Supreme Court filing, said the changes would have enormous consequences for more than 100 million U.S. Android users and 500,000 developers.

Google said it plans to file a full appeal to the Supreme Court by October 27, which could allow the justices to take up the case during their nine-month term that began on Monday.

Epic has said Google is relying on what it called "flawed security claims" to justify its control over Android devices.

Epic had urged the justices to allow Donato's injunction to take effect "so consumers and developers can benefit from competition, choices and lower prices."

In July, a three-judge panel of the San Francisco-based 9th U.S. Circuit Court of Appeals upheld the injunction, ruling that the record in Epic's lawsuit was "replete with evidence that Google's anticompetitive conduct entrenched its dominance."

Google faces other lawsuits from government, consumer and commercial plaintiffs challenging its search and advertising business practices.