In one of the most important cases of the social media age, free speech and national security collide at the Supreme Court on Friday in arguments over the fate of TikTok, a wildly popular digital platform that roughly half the people in the United States use for entertainment and information.

TikTok says it plans to shut down the social media site in the U.S. by Jan. 19 unless the Supreme Court strikes down or otherwise delays the effective date of a law aimed at forcing TikTok’s sale by its Chinese parent company.

Working on a tight deadline, the justices also have before them a plea from President-elect Donald Trump, who has dropped his earlier support for a ban, to give him and his new administration time to reach a “political resolution” and avoid deciding the case. It’s unclear if the court will take the Republican president-elect’s views — a highly unusual attempt to influence a case — into account.

TikTok and China-based ByteDance, as well as content creators and users, argue the law is a dramatic violation of the Constitution’s free speech guarantee.

“Rarely if ever has the court confronted a free-speech case that matters to so many people,” lawyers for the users and content creators wrote. Content creators are anxiously awaiting a decision that could upend their livelihoods and are eyeing other platforms.

The case represents another example of the court being asked to rule about a medium with which the justices have acknowledged they have little familiarity or expertise, though they often weigh in on meaty issues involving restrictions on speech.

The Biden administration, defending the law that President Joe Biden signed in April after it was approved by wide bipartisan majorities in Congress, contends that “no one can seriously dispute that (China’s) control of TikTok through ByteDance represents a grave threat to national security.”

Officials say Chinese authorities can compel ByteDance to hand over information on TikTok’s U.S. patrons or use the platform to spread or suppress information.

But the government “concedes that it has no evidence China has ever attempted to do so,” TikTok told the justices, adding that limits on speech should not be sustained when they stem from fears that are predicated on future risks.

In December, a panel of three appellate judges, two appointed by Republicans and one by a Democrat, unanimously upheld the law and rejected the First Amendment speech claims.

Adding to the tension, the court is hearing arguments just nine days before the law is supposed to take effect and 10 days before a new administration takes office.

In language typically seen in a campaign ad rather than a legal brief, lawyers for Trump have called on the court to temporarily prevent the TikTok ban from going into effect but refrain from a definitive resolution.

“President Trump alone possesses the consummate dealmaking expertise, the electoral mandate, and the political will to negotiate a resolution to save the platform while addressing the national security concerns expressed by the Government — concerns which President Trump himself has acknowledged,” D. John Sauer, Trump’s choice to be his administration’s top Supreme Court lawyer, wrote in a legal brief filed with the court.

Trump took no position on the underlying merits of the case, Sauer wrote. Trump’s campaign team used TikTok to connect with younger voters, especially male voters, and Trump met with TikTok CEO Shou Zi Chew at Trump’s Mar-a-Lago club in Palm Beach, Florida, in December. He has 14.7 million followers on TikTok.

The justices have set aside two hours for arguments, and the session likely will extend well beyond that. Three highly experienced Supreme Court lawyers will be making arguments. Solicitor General Elizabeth Prelogar will present the Biden administration’s defense of the law, while Trump’s solicitor general in his first administration, Noel Francisco, will argue on behalf of TikTok and ByteDance. Stanford Law professor Jeffrey Fisher, representing content creators and users, will be making his 50th high court argument.

If the law takes effect, Trump’s Justice Department will be charged with enforcing it. Lawyers for TikTok and ByteDance have argued that the new administration could seek to mitigate the law’s most severe consequences.

But they also said that a shutdown of just a month would cause TikTok to lose about one-third of its daily users in the U.S. and significant advertising revenue.