Elizabeth Prelogar, the lawyer representing the US government, is mainly arguing that because TikTok is owned by a "foreign adversary", it would be weaponised to harm the US and its interest.

Chief Justice John Roberts brings up a point made earlier, which is that "ByteDance might be through TikTok trying to get Americans to argue with each other?"

"If they do, then I say they're winning," Roberts says - a comment that drew laughter from both Prelogar and those in attendance.

Prelogar then argues that China looks for every opportunity to weaken the US. If it has control over TikTok - "a key communications channel" - it is hard to predict how it can use it as a tool to harm American interests.

"We know the PRC [People's Republic of China] has a veracious appetite to get its hands on as much information about Americans as possible," she adds, referring to TikTok as a "potent weapon" that can be used to that effect.

Judges are pressing the US government about why Chinese ownership is a risk, saying "everybody now knows" about its role.

Kagan notes that TikTok has said it is even willing to have a disclosure on its website warning of the government's concerns. Others press on what the implications would be for foreign-owned publications, like newspapers.

But Prelogar says: "Americans are on this platform thinking they are speaking to one another."

She says it is important that alleged Chinese activities are "covert", saying a blanket warning "doesn't put anyone on notice as to when that influence is actually happening".

Fisher finishes up on behalf of content creators.

Then, it's Elizabeth Prelogar, the US Solicitor General, who represents the government.

She immediately says that the Chinese government's control of TikTok poses a "grave threat" to national security.

She says that there is no dispute that China compels companies like ByteDance to secretly turn over data.

This means, she says, that the Chinese government could "weaponise" TikTok at any time to harm the US.

Prelogar says the Chinese government is building "detailed profiles" about Americans, with this data set becoming a "powerful tool" to be used against them.

And, she denies that the Act focuses on banning certain types of content, saying that it is narrowly tailored to address national security threats.

"The Act leaves all of that speech unrestricted once TikTok is freed from foreign adversary control," she adds.

Justine Samuel Alito floats the idea of whether some other social media company could come in and fill the void left by TikTok should it be banned in the US - one that would allow Americans to still make content and profit off of it.

Fisher, the lawyer for content creators, responds by saying that many of his clients have tried to post on other platforms to generate the same audience and engagement they have received on TikTok, but have been unable to do so.

Justice Alito then asks if the creators' attachment to TikTok is sentimental, like how one might feel about "an old article of clothing".

"Empirically, other companies have been trying for a few years to catch up with TikTok and replicate it," Fisher notes. "But they have been unsuccessful, and that ought to tell you something."

Kagan is testing Fisher about whether the First Amendment rights of Americans can reasonably be extended to TikTok, given that it is owned by a foreign corporation.

"it doesn't matter that Americans want to work with ByteDance because ByteDance is a foreign corporation which doesn't have First Amendment rights," she says.

But Fisher says he thinks that's not quite right, comparing creators who want to use TikTok's algorithm to a bookstore that wants to sell a book.

"The Communist manifesto written by Karl Marx has no first amendment standing on its own in America but if a bookstore wants to sell that publication, I don't think Congress can prevent it from doing so," he says.

They don't get into national security issues, which might complicate that picture.

Fisher brings up the platform Temu, and says it is "curious" why TikTok alone is being singled out when Americans' data is put at risk by other sites.

But he's then challenged by Justice Sotomayor on how many of these sites have the same data collection mechanisms that TikTok does.

Fisher says that other websites are taking "much the same kind of information if not more".

The pair then go back and forth on this, before Sotomayor asks why TikTok argues that issues of data security can't be separated from the issue of TikTok's algorithm.

The lawyer says that congress is within its right to pass a data security law separately, but says that even if the law goes through, TikTok gets to keep all of the data anyway.

So, he says, wouldn't a law acting purely on data security interests also require them to expunge this data?

Chief Justice Roberts challenges Fisher's contention that this law threatens the rights of Americans to express themselves.

"Congress is fine with expression. They're not fine with a foreign adversary as they've determined it is gathering all this information," he says.

But Fisher says there are two issues that the court should consider separately - and this law would be different if data collection were the only concern.

He maintains that Congress was driven by its worries about the content, noting that the record shows lawmakers were worried about how the algorithm might be used to influence what people think.

"The only thing that can affect national security is the substance of videos," he says.

Fisher is asked by Justice Ketanji Brown Jackson whether Congress should be able to prohibit Americans from associating with foreign entities that are considered hostile to the US.

He responds that when it comes to national security, Congress can prohibit Americans with associating with "terrorist organisations" or others that can put US security at risk.

But he argues that this case is "fundamentally different".

"What the government tells you - in its own brief - that it is worried here about the ideas that might be expressed on TikTok," Fisher says, including undermining US leadership or sowing doubts about democracy, or influencing people to have "pro-China" views.

He argues that the position by the government to ban TikTok for this goes against US precedent.

"It's not enough to say national security," he adds, saying that government has to outline in detail what is the real harm at play here.

Setting out his argument, Fisher relies on Americans' rights of free speech, and draws on some historic principles that have led the country's development.

He says that the country has historically faced "ideological campaigns by foreign adversaries", but he says that under the First Amendment, mere ideas do not represent a national security threat.

Restricting speech because it might sew doubt about our leaders or undermine democracy are the kind of things our enemies do, he says.

He's then asked how the ban would restrict content creators' free speech, as the law doesn't mention anything about the users of TikTok.

"American creators have a right to work with publishers of their choice," he replies, suggesting that closing down TikTok would hinder this choice.

The Supreme Court Justices have just wrapped up their questioning of Noah Francisco, the lawyer representing TikTok in this hearing.

They are now listening to arguments being laid out by another lawyer - Jeffrey Fisher - who is representing TikTok creators.

Fisher starts by saying that that the "act directly restricts the First Amendment rights of American creators to participate and speak in what the Court called a little less than a decade ago 'the modern public square'".

Complex questions for TikTok's Franciscopublished at 16:28 Greenwich Mean Time

16:28 GMT

Liv McMahon
Technology reporter

The questions put to Noel Francisco, TikTok and ByteDance’s lawyer, today by Supreme Court justices highlighted the many questions at the heart of this case – that of TikTok and ByteDance’s corporate structure, whether TikTok’s algorithm is itself a form of speech and why TikTok cannot be divested.

Many of these were intermingled with questions over both companies' relationship to the Chinese government – concerns over which paved the way to the passage of the law in the first place.

Concerns about the collection and security of US user data were highlighted by several justices. And at times, Francisco acknowledged some of the risks and concerns he was being asked about.

But he maintained throughout his responses to the court’s nine justices that the law requiring TikTok’s sale or ban would be a "direct burden" on its free speech, returning to this even when needled on separate, particular issues by justices.

But justices Jackson and Barrett questioned whether it was more about TikTok’s association with ByteDance – something that could be solved by selling off the company.

"We wouldn’t be here" if that had happened, said Justice Barrett.

Justice Brett Kavanaugh has drilled into TikTok about the concerns that the US government has raised about the data the app collects on its users, and how it might be used.

He says the law reflected concerns that China could use that information over time to develop spies or blackmail young people who - a generation from now - might be working for agencies like the FBI.

"Is that not a realistic assessment?" he asks.

"I'm not disputing the risks. I'm disputing the means they've chosen" to address that, TikTok's lawyer, Francisco replies.

He says Congress should have considered an "obvious alternative" to this law - a measure that would prohibit the sharing of that data.

Kavanaugh says the risks related to data collection seems like a "huge concern for the future of the country".

"It is a concern that can be addressed directly," Francisco insists. We have to "at least consider the consequences of shutting down a speech platform used by 170 million Americans".

Justice Ketanji Brown Jackson now suggests that the case might not concern free speech after all, but the ability of one business, TikTok, to associate with another, ByteDance.

What you're really complaining about is the inability to associate with ByteDance and its algorithm, Justice Ketanji Brown Jackson suggests.

She suggests that TikTok can continue to operate and run its own algorithm as long as it separates itself from ByteDance.

"Isn't this really just all about association?" she asks.

Francisco says that she is partly correct, but emphasises that the law is a "direct restriction on TikTok's speech" because it prevents them from continuing in the way they would like - using ByteDance's algorithm - and it would therefore have to find an alternative type of speech, by essentially finding a new way of curating its content.

Justice Kavanaugh asks Francisco what happens if this law goes through.

We go dark and stop operating on January 19, he says.

"That's why a short reprieve here would make all the sense in the world," he says, given how big of a decision this is.

But January 19 is only one day before Trump takes office - and we might be in a different world by then, Francisco says. Trump might intervene to change something, he says, though this demand for Chinese parent company ByteDance to divest from TikTok was passed by Congress.

Justice Amy Coney Barrett then pushes back and says that TikTok does not necessarily have to shut down, if ByteDance were willing to divest from TikTok as the US law demands.

Francisco says it would be a major burden to transfer the ByteDance algorithm source code to TikTok.

Any new TikTok "would be a fundamentally new platform" without ByteDance's algorithm, he says.

Justice Kavanaugh raises the government's concern that China is gathering information on Americans, and this data could then be used to influence them in the future.

"Is this not a realistic assessment by Congress and the president of the risks here?" he asks.

Francisco responds: "I'm not disputing the risks."

But, he goes on to describe how TikTok's data is stored in servers in Virginia, and explains how the app is unable to share this sensitive user data with anyone.

He says that congress needs to consider the alternative to shutting down a speech platform used by 170 million Americans; for instance threats of punishment for TikTok employees who share the data illegally.

He says these alternatives have not been properly considered by the court yet.

Francisco is now fielding questions again by Justice Sonia Sotomayor. She asks if TikTok considers this a "speech" issue or a "data control" issue, and if their arguments would be different if it is the latter.

Francisco responds by saying that their arguments would be "very similar" in that case.

Justice Sotomayor then asks if TikTok’s argument is that Congress should have looked at alternatives to the ban.

TikTok's lawyer says that there is nothing in the record to suggest that the government ever considered "a law that simply prohibits TikTok" from sharing sensitive data with ByteDance or anyone else, instead of outright banning it.

Sotomayor asks about "covert manipulation" of the platform, which was asked about earlier, and what burden TikTok USA has to address that.

Justice Elena Kagan, one of the court's liberal justices, seems sceptical that TikTok's First Amendment rights are threatened by the law, arguing that the target appears to be ByteDance, a foreign company.

"What's the problem here?" she asks.

"The law is only targeted at this foreign corporation, which doesn't have first amendment rights. Whatever effect it has, it has," she adds.

Francisco says there is a wider universe of entities - including creators - whose rights are threatened.

We're deep into the weeds of the app's algorithm and a discussion of whether the ban represents a speech-based restriction.

Justice Elena Kagan interjects, and asks more simply how TikTok's first amendment rights are being impacted.

Francisco replies that "TikTok wants to speak", and it will be unable to do so in ten days unless ByteDance sells up.

Justice Amy Coney Barrett, a Trump-pick for Supreme Court, asks TikTok’s lawyer if the platform’s algorithm can qualify as a form of "speech".

Francisco responds: "Yes," adding that "the algorithm is a lot of things. It is basically how we predict what our customers want to see".

Justice Barrett then states that the concern here is about the "covert content manipulation" of the algorithm, and whether that is being directed by ByteDance.

The platform’s lawyer responds that TikTok "absolutely resists any type of content manipulation by China".

He adds that if all the government is concerned about is covertness, then a simple solution is to do a "risk disclosure" - essentially disclose publicly that there may be risks to using the platform.

Francisco then argues that the government’s worry essentially is that TikTok will be used to promote content in the future that is "somehow critical of the US", saying this proves that this is a "content-based restriction".

TikTok and ByteDance have argued since the law was passed in April that requiring the app’s sale to a non-Chinese company would be near impossible to do within a 270 day timeframe – saying this amounted to an effective ban.

Asked by justice Neil Gorsuch today if TikTok’s divestiture would be feasible under "any timeframe", TikTok’s lawyer Noel Francisco says it would be "extraordinarily difficult".

The way that the law’s “qualified divestiture” request has been interpreted, he says, would appear to prevent any kind of global coordination between its engineers across the world who maintain and update its source code – TikTok’s technical underpinnings that keep it running.

He said they would also need to be able to access global content. “We understand that couldn’t happen,” he adds.