The top court is holding oral arguments in the case nine days before TikTok faces a ban unless ByteDance divests from the popular app.

Signed by President Joe Biden in April, the law would block TikTok from US app stores and web hosting services unless ByteDance sells its stake by January 19.

The US government alleges TikTok allows Beijing to collect data and spy on users and is a conduit to spread propaganda. China and ByteDance strongly deny the claims.

TikTok is arguing that the law -- the Protecting Americans from Foreign Adversary Controlled Applications Act -- violates its First Amendment rights.

"We believe the Court will find the TikTok ban unconstitutional so the over 170 million Americans on our platform can continue to exercise their free speech rights," a TikTok spokesman said.

In a filing with the Supreme Court, TikTok said "Congress has enacted a massive and unprecedented speech restriction" that would "shutter one of America's most popular speech platforms."

"This, in turn, will silence the speech of Applicants and the many Americans who use the platform to communicate about politics, commerce, arts, and other matters of public concern," it added.

The potential ban could strain US-China relations just as Donald Trump prepares to be sworn in as president on January 20.

Trump, who has 14.7 million followers on TikTok, has emerged as an unlikely ally of the platform in a reversal from his first term, when the Republican leader tried to ban the app, citing national security concerns.

Trump's lawyer, John Sauer, filed a brief with the Supreme Court last month asking it to pause the law.

In the amicus curiae -- or "friend of the court" -- brief, Sauer made it clear the president-elect does not take a position on the legal merits of the current case.

"Instead, he respectfully requests that the court consider staying the act's deadline for divestment of January 19, 2025... thus permitting President Trump's incoming Administration the opportunity to pursue a political resolution of the questions at issue in the case," Sauer said.

- 'You need competition' -

The president-elect met with TikTok chief executive Shou Zi Chew at his Mar-a-Lago residence in Florida in December.

Trump told Bloomberg recently he had changed his mind about the app.

"Now (that) I'm thinking about it, I'm for TikTok, because you need competition," he said.

A coalition of free speech groups -- including the influential American Civil Liberties Union -- filed a separate brief with the Supreme Court opposing the law, citing censorship concerns.

"Such a ban is unprecedented in our country and, if it goes into effect, will cause a far-reaching disruption in Americans' ability to engage with the content and audiences of their choice online," they said.

In an 11th hour development on Thursday, US billionaire Frank McCourt, founder of the non-profit Project Liberty, announced that he had put together a consortium to acquire TikTok's US assets from ByteDance.

"We've put forward a proposal to ByteDance," McCourt said in a statement. "We look forward to working with ByteDance, President-elect Trump, and the incoming administration to get this deal done."

AFP, among more than a dozen other fact-checking organizations, is paid by TikTok in several countries to verify videos that potentially contain false information.