TikTok has lost an appeal against plans to ban the video-sharing app in the US.
The social media platform had argued the proposal was a breach of the US First Amendment, which protects freedom of speech.
TikTok pushed to overturn a law that could lead to its ban in a few months.
However, the petition was dismissed on Friday by the US Court of Appeals for the District of Columbia Circuit.
Its judges ruled the government’s ban was constitutional because it was designed “solely to protect that freedom from a foreign adversary nation and to limit that adversary’s ability to gather data on people in the United States”.
The law, which was signed off by US President Joe Biden in April, requires TikTok to break ties with its China-based parent company ByteDance by mid-January – or else it will be blocked in the country.
It was introduced following concern from some US politicians that the company might share user data with the Chinese government, despite repeated assurances from the firm that it would not.
Critics have also expressed fears that Chinese authorities may be able to manipulate TikTok’s algorithms, shaping what content users see and are influenced by. This claim is also denied.
TikTok and ByteDance are now set to launch another appeal to the US Supreme Court.
However, the two firms could also be thrown a lifeline by Donald Trump, who is due to be sworn in as president on 20 January.
Despite trying to introduce his own TikTok ban during his first term as president, the Republican has since changed his mind.
He said during the 2024 presidential campaign that he wanted to “save” the app and expressed concern that a ban would help its rival Facebook.
Mr Trump also signed up to TikTok and currently has more than 14 million followers on the site, although he has not posted anything since his election victory.
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Reacting to Friday’s court ruling, a TikTok statement said: “The Supreme Court has an established historical record of protecting Americans’ right to free speech, and we expect they will do just that on this important constitutional issue.
“Unfortunately, the TikTok ban was conceived and pushed through based upon inaccurate, flawed and hypothetical information, resulting in outright censorship of the American people.”
It added: “The TikTok ban, unless stopped, will silence the voices of over 170 million Americans here in the US and around the world on 19 January 2025.”
Similar security concerns over TikTok prompted ministers in the UK to ban the app from government phones in March last year.
Some 13 US states and Washington DC also launched legal action against the social media platform in October, alleging it was harming children’s mental health and was not doing enough to protect them.
TikTok dismissed the claims as “inaccurate and misleading”.