Justices Sonia Sotomayor and Neil M. Gorsuch wrote separately, agreeing with the court’s judgment about the constitutionality of the law but expressing some concerns.

The unanimous decision was a major blow for TikTok, injecting deep uncertainty into the app’s future with the deadline to sell the platform just two days away. President-elect Donald Trump, who has vowed to use his power to “save” the app, will be sworn into office a day later.

No U.S. law has ever shut down a popular social media platform before, let alone one with more than 170 million users in the United States who rely on the app for news, entertainment and self-expression.

Trump had asked the Supreme Court to delay implementation of the law to give him an opportunity to act once he returns to the White House. With the court declining that option and no sale of the app seemingly imminent, the ban is now poised to take effect the day before Trump’s inauguration.

The court’s unsigned, 20-page decision said the ban-or-sale law does not violate the free speech rights of millions of TikTok users in the United States. The law was passed in April with bipartisan support and signed by President Joe Biden in response to national security concerns about the Chinese government’s potential influence over the platform.

In response to the court’s decision, White House press secretary Karine Jean-Pierre said that Biden believes “TikTok should remain available to Americans,” but under new ownership and that implementing the law “must fall to the next Administration.”

The justices said the U.S. government was justified in singling out TikTok and its China-based parent company, ByteDance, writing that the app’s “scale and susceptibility to foreign adversary control, together with the vast swaths of sensitive data the platform collects, justify differential treatment.”

Trump, who said Friday he discussed TikTok with Chinese President Xi Jinping, said in a social media post that the court’s decision was expected and “everyone must respect it.” His decision about the app’s fate, he added, “will be made in the not too distant future, but I must have time to review the situation.”

Under the TikTok law, known as the Protecting Americans From Foreign Adversary Controlled Applications Act, app-store giants such as Google and Apple and internet-hosting services could face massive fines if they continue to carry TikTok on their products beyond the Sunday deadline for divestment. Infractions could cost companies $5,000 for each user that continues to access TikTok, which could add up to billions of dollars in penalties.