The law—which prohibits U.S. app stores from hosting TikTok unless Chinese parent company ByteDance divests from it—is scheduled to take effect one day before Trump’s Jan. 2

Congress says the popular video app poses a looming threat to the nation’s security because of its Chinese owner. What the justices decide could determine if the app is shut down.

TikTok ran into a wave of skepticism Friday when it urged the Supreme Court to strike down a law that could end its presence in the U.S. in one of the most high-profile standoffs of the social media era.