TikTok and its Chinese owner, ByteDance, got their day in court on Monday, telling a federal appellate panel that a new law to force the short-video app’s sale or else see it banned in the US was unconstitutional and a violation of its users’ free speech rights.

The three-judge panel at the US Court of Appeals for the District of Columbia heard the oral arguments in a case challenging the law, signed by US President Joe Biden this spring.

Monday’s arguments came amid mounting national security concerns over Chinese ownership of the platform, which is used by 170 million Americans, and clashes in Congress and the courts over thorny questions about online free speech.

While TikTok has won legal victories against earlier bids to ban it in the US, this was the first time it is challenging a federal law.

“This law imposes extraordinary speech prohibition based on indeterminate future risks,” Andrew Pincus, the lawyer for TikTok, told the court, adding that TikTok US was an American company and that ByteDance was registered in Cayman Islands.

He said that in targeting TikTok, the government – which contends that the app, with the data it collects about its American users, is a national security risk – was basing its threatened ban on something that had not happened yet but might some day.

Chief Judge Sri Srinivasan, head of the panel, however, noted that TikTok remained “subject to Chinese control”.

If TikTok were a wholly owned US company, he said, “there’s no doubt that would be a huge First Amendment concern”, but he added that was not the case, because the law targets TikTok’s foreign ownership and foreign manipulation of content.

Senior Circuit Judge Douglas Ginsburg also dismissed the claim about TikTok being “singled out”, calling it a “blinkered view”.

The law, he said, “describes a category of companies, all of which are owned by or controlled by adversary powers, and subjects one company to an immediate necessity”.

Ginsburg noted that two years of negotiations between the US and TikTok had failed to reach agreement on a national security arrangement.

Ginsburg also observed that TikTok’s curation was “not entirely” done in the US, prompting Pincus to say that changes were made to the recommendation engine, a tool that uses machine learning to suggest the most relevant items to users.

When Ginsburg asked if these changes came from Beijing, Pincus responded that some of the content moderation is done in the US.

Pincus also argued for “less restrictive” means to deal with the security concerns, such as TikTok providing more disclosures about its data and content curation.

Circuit Judge Neomi Rao responded that disclosure could depend on TikTok’s “voluntary cooperation”.

Pincus replied that there was no “imminent” threat shown as a “factual matter”.

Jeffrey Fisher, representing a group of TikTok content creators, argued that the law dictates whom those creators can work with.

“Our interest is in working with the publisher and editor of our choice, including the current ownership, which works very well for our creators,” he said.

“Once that speech is directed into the United States,” Fisher added, “and certainly once that speech is in concert with other Americans and indeed propagated by other Americans, the speech on TikTok is not Chinese speech.”

Daniel Tenny of the Justice Department contended that data collected by TikTok contained “patterns” and “content” that made it “quite valuable for a foreign adversary”.

He added that this information could be used to “influence” users to get involved in intelligence activities; the US, he said, does not want China “in charge” of what the platform churns out.

The “core point” of the law, Tenny said, was TikTok’s code is “made in China”. He added that TikTok’s content moderation “is not expression by Americans in America, it is expression by Chinese engineers in China”.

Tenny noted that when Congress passed the bill and Biden signed it into law, their intent was to address possible foreign-content manipulation – and not attack free speech. He described any impact on free speech as “incidental” to the law’s objective.

“The whole point is that it’s covert, and we don’t have a way to stop it from being covert, because it’s being done on through incredibly complex computer code that no one – including Oracle, who they want to hire – would understand.”

“It’s being done in a foreign nation where … we can’t pass a law saying ByteDance make this or that disclosure about their internal operations because they’re off in China,” Tenny added.

After Biden signed the bill into law in April directing ByteDance to find a non-Chinese buyer for TikTok or face a ban, the company was given until January 2025 to make a decision.

Following the law’s passage, ByteDance and TikTok, along with several users of the app, filed their federal suit to block it.

All parties asked the panel for a ruling by December to ensure enough time for the losing party to seek a review from the US Supreme Court before the law goes into effect, which is set for January 19.

US officials have warned for years that Beijing could gain access to TikTok’s user data or manipulate content on the app through its influence over ByteDance. In 2020, then-president Donald Trump tried to force a sale of TikTok or ban it by executive action, but that was foiled by legal challenges.

This year, Trump reversed himself, supporting TikTok after meeting with a billionaire Republican donor, Jeffrey Yass, who owns a large stake in ByteDance; Trump now argues that a ban would only help TikTok’s rival, Meta.

Both the Trump and Kamala Harris presidential campaigns have TikTok accounts.

TikTok’s suit centred on free speech protections in the US Constitution’s First Amendment, but it also made arguments related to due process and private property rights enshrined in the Fifth Amendment, as well as constitutional protections against a “bill of attainder”– a legislative act that punishes an individual or group without a trial.

The company has said that it is “technologically, commercially, and legally infeasible” to divest its operations. Beijing has signalled that it would not allow the export of the recommendation algorithm that TikTok says is key to its success in the US.

There has been no public evidence of the Chinese government requesting data about Americans or manipulating content on the app, and the company has denied it has ever turned over such data. But the Biden administration says the company’s ownership structure made such risks too great.

The White House has said that it seeks the sale of TikTok, not a ban of the app.

TikTok developed a plan it said would secure American user data without requiring the sale of the company, but Washington officials were unmoved.

In their lawsuit, ByteDance and TikTok said they had spent more than US$2 billion to put the plan into action and made additional commitments in a 90-page draft national security agreement developed with the Committee on Foreign Investment in the United States (CFIUS), an inter-agency group in charge of reviewing national security implications of foreign investments.

That agreement, according to the suit, included a “shut-down option” that would give the federal government the authority to suspend TikTok in the US if it violated certain obligations.

After Monday’s nearly two-hour hearing, TikTok content creators and small business owners who are petitioners in the case spoke with reporters.

Kiera Spann, an influencer with more than 770,000 followers, said she believed the ban was “not about data security”, suggesting that if Congress “truly” cared about data protection it would not have “singled out” TikTok.

Paul Tran, owner of skincare brand Love and Pebble with over 140,000 followers, said that other platforms like Facebook and Instagram were “just not the same” and attempts to grow on those had “almost shut our business”.

Before oral arguments, free speech groups filed amicus briefs in support of TikTok, while some Hong Kong and Uygur human rights groups, think tanks and lawmakers filed in support of the government.

Some groups have taken issue with the evidence being used in the government’s claim, which included heavily redacted documents.

“The ban is problematic in itself, but the government’s contention that it should be upheld on the basis of secret evidence is fundamentally undemocratic,” said Xiangnong Wang, a staff lawyer at the Knight First Amendment Institute at Columbia University.