TikTok and its parent company ByteDance have sued to block a law signed by Joe Biden just weeks ago that would force the sale of the short video app or ban it from the US.

The companies filed a lawsuit on Tuesday against the US government in the court of appeals for the District of Columbia, arguing the law is unconstitutional and violates free speech protections.

Signed by the president on 24 April as part of a broader foreign aid package, the law gives China’s ByteDance until 19 January 2025 to sell TikTok to an approved buyer. If it does not, the US would prohibit app stores from offering TikTok and bar internet hosting services from supporting TikTok.

The companies argue in the suit that the divestiture required by the bill “is simply not commercially, legally, or technically possible.

“There is no question: the Act (law) will force a shutdown of TikTok by January 19, 2025, silencing the 170 million Americans who use the platform to communicate in ways that cannot be replicated elsewhere,” the suit said.

The suit confirmed previous reports that ByteDance would not sell TikTok without the powerful recommendation algorithm that has fueled the platform’s success. The Chinese government “has made clear that it would not permit a divestment of the recommendation engine that is a key to the success of TikTok in the United States”, the suit said.

The potential for a ban of TikTok has been escalating since Donald Trump first unsuccessfully attempted to block it in 2020. Critics of TikTok have expressed worry that the platform’s China-based parent company could collect sensitive user data and censor content that goes against the Chinese government – claims TikTok denies.

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Amid the political fallout, TikTok spent more than $2bn to implement measures to protect the data of US users, according to the suit. The suit also highlighted additional commitments the company made in a 90-page draft National Security Agreement developed through negotiations with the Committee on Foreign Investment in the United States (CFIUS), an interagency committee, chaired by the US Treasury Department, that reviews foreign investments in American businesses that implicate national security concerns.

CFIUS had been in talks with TikTok to find solutions, though the agreement included TikTok agreeing to a “shut-down option” that would give the US government the authority to suspend TikTok in the US if it violated some obligations”, according to the suit.

But in August 2022, according to the lawsuit, CFIUS stopped engaging in meaningful discussions about the agreement and in March 2023 CFIUS “insisted that ByteDance would be required to divest the US TikTok business”.

Many experts have questioned whether any potential buyer possesses the financial resources to buy TikTok and if China and US government agencies would approve a sale. To move the TikTok source code to the US “would take years for an entirely new set of engineers to gain sufficient familiarity”, according to the lawsuit.

Under the current law, Biden could extend the 19 January divestiture deadline by three months if he determines ByteDance is making progress.