WASHINGTON (Reuters) -TikTok warned late Friday it will go dark in the United States on Sunday unless President Joe Biden's administration provides assurances to companies like Apple and Google that it will not face enforcement actions when a ban takes effect.

The statement came hours after the Supreme Court upheld a law banning TikTok in the United States on national security grounds if its Chinese parent company ByteDance does not sell it, putting the popular short-video app on track to go dark in just two days.

The court's 9-0 decision throws the social media platform - and its 170 million American users - into limbo, and its fate in the hands of Donald Trump, who has vowed to rescue TikTok after returning to the presidency on Monday.

"Unless the Biden Administration immediately provides a definitive statement to satisfy the most critical service providers assuring non-enforcement, unfortunately TikTok will be forced to go dark on January 19," the company said.

The White House declined to comment.

Apple, Alphabet's Google, Oracle and others could face massive fines if they continue to provide services to TikTok after the ban takes effect.

The law was passed by an overwhelming bipartisan majority in Congress last year and signed by Biden, though a growing chorus of lawmakers who voted for it are now seeking to keep TikTok operating in the United States.

TikTok, ByteDance and some of the app's users challenged the law, but the Supreme Court decided that it did not violate the U.S. Constitution's First Amendment protection against government abridgment of free speech as they had argued.

ByteDance has done little to divest of TikTok by the Sunday deadline set under the law. But the app's shutdown might be brief. Trump, who in 2020 had tried to ban TikTok, has said he plans to take action to save the app.

"My decision on TikTok will be made in the not too distant future, but I must have time to review the situation. Stay tuned!" Trump said in a social media post.

TikTok CEO Shou Zi Chew plans to attend Trump's second inauguration on Monday in Washington.

Trump said he and Chinese President Xi Jinping discussed TikTok in a phone call on Friday.

'FOREIGN ADVERSARY CONTROL'

For years TikTok's Chinese ownership has raised concerns among U.S. leaders, and the TikTok fight has unfolded at a time of rising trade tensions between the world's two biggest economies.

Lawmakers and Biden's administration have said China could use TikTok to amass data on millions of Americans for harassment, recruitment and espionage.

"TikTok's scale and susceptibility to foreign adversary control, together with the vast swaths of sensitive data the platform collects, justify differential treatment to address the government's national security concerns," the Supreme Court said in the unsigned opinion.

TikTok has become one of the most prominent social media platforms in the U.S., particularly among young people who use it for short-form videos, including many who use it as a platform for small businesses.

Some users reacted with shock that the ban could actually happen.

"Oh my god, I'm speechless," said Lourd Asprec, 21, of Houston, who has amassed 16.3 million followers on TikTok and makes an estimated $80,000 a year from the platform. "I don't even care about China stealing my data. They can take all my data from me. Like, if anything, I'll go to China myself and give them my data."

The company's powerful algorithm, its main asset, feeds individual users short videos tailored to their liking. The platform presents a vast collection of user-submitted videos, that can be viewed with a smart phone app or on the internet.

As the Jan. 19 deadline approached, millions of users jumped to other Chinese-owned apps like RedNote, finding they had to decipher its all-Mandarin platform to kickstart their feeds.

"China is adapting in real-time to the ruling," said Craig Singleton, a China expert at the Foundation for Defense of Democracies think tank, which submitted a brief in the case against TikTok. "Beijing isn't just building apps; it's building a discourse power ecosystem to shape global narratives and influence societies."

Attorney General Merrick Garland said in a statement the ruling affirmed that the law protects U.S. national security.

"Authoritarian regimes should not have unfettered access to millions of Americans' sensitive data," Garland added.

WHAT HAPPENS NEXT

The Biden administration has emphasized that TikTok could continue operating if it is freed from China's control. The White House said on Friday that Biden will not take any action to save TikTok.

Biden has not formally invoked a 90-day delay in the deadline as allowed by the law.

"This decision's going to be made by the next president anyway," Biden told reporters.

The law bars providing certain services to TikTok and other foreign adversary-controlled apps including by offering it through app stores such as Apple and Google.

Google declined to comment on Friday. Apple and Oracle did not respond to requests for comment.

White House Press Secretary Karine Jean-Pierre said action to implement the law "must fall to the next administration" while the Justice Department said "implementing and ensuring compliance with the law after it goes into effect on January 19 - will be a process that plays out over time."

TikTok said those statements "have failed to provide the necessary clarity and assurance to the service providers that are integral to maintaining TikTok's availability to over 170 million Americans."

A viable buyer could still emerge, or Trump could invoke a law called the International Emergency Economic Powers Act, stating that keeping TikTok is beneficial for national security.

Only one notable bidder has emerged so far - Frank McCourt, former owner of the Los Angeles Dodgers baseball team, who said he believes TikTok is worth about $20 billion without its algorithm.

"Beijing needs TikTok more than Washington does," said Michael Sobolik, a senior fellow and expert in U.S.-China relations at the Hudson Institute think tank.

"With that leverage, Trump has a better chance of getting what he wants: TikTok's continued operation in America without any national security threats."