The US Supreme Court has unanimously upheld a law banning TikTok starting on Sunday, unless the app is sold by its China-based parent company ByteDance.
The move is a major blow to a platform used by nearly half of all Americans.
A sale does not appear imminent and, although experts have said the app will not disappear from existing users' phones once the law takes effect, new users will not be able to download it and updates will not be available.
That will eventually render the app unworkable, the US Justice Department has said in court filings.
"There is no doubt that, for more than 170 million Americans, TikTok offers a distinctive and expansive outlet for expression, means of engagement, and source of community. But Congress has determined that divestiture is necessary to address its well-supported national security concerns regarding TikTok's data collection practices and relationship with a foreign adversary," the Supreme Court said in the unsigned opinion.
The court added that "we conclude that the challenged provisions do not violate petitioners' First Amendment rights."
The US has said it is concerned about TikTok collecting vast swaths of user data, including sensitive information on viewing habits, that could fall into the hands of the Chinese government through coercion.
But the app has responded by saying that no evidence has been released showing that China has attempted to manipulate content on its US platform.
Officials have also warned the algorithm that fuels what users see on the app is vulnerable to manipulation by Chinese authorities, who can use it to shape content on the platform in a way that is difficult to detect.
TikTok allows users to watch hundreds of videos in about half an hour because some are only a few seconds long, but experts have raised fears that is addictive and can have a negative mental health impact for children. The app has said these claims are inaccurate.
The White House said on Friday that Tiktok should remain available to Americans but the timing of the Supreme Court ruling on a law banning the app means it must fall to the Trump administration.
"TikTok should remain available to Americans, but simply under American ownership or other ownership that addresses the national security concerns identified by Congress in developing this law," a statement read.
