TikTok faces an uphill battle to avoid a US ban if its Chinese owner doesn’t sell the wildly popular social media app, judging from a grilling by an appellate court panel.

TikTok faced off with the U.S. government in federal court on Monday, arguing a law that could ban the platform in a few short months is unconstitutional while the Justice Department said it is needed to eliminate a national security risk posed by the popular social media company.

TikTok on Monday pushed back against a law that would force the popular video app to sell to a non-Chinese owner or be banned, in what is shaping up to be a landmark case.