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.

The Supreme Court seemed inclined on Friday to uphold a law that would force a sale or ban the popular short-video app TikTok in the United States by Jan. 19, with the justices focusing on the national security concerns about China that prompted the crackdown.

A majority of the justices appeared more concerned about the national security implications of the popular app’s Chinese ownership than about the restrictions on free speech the law would impose.