TikTok and its owner ByteDance are fighting to keep the popular app online in the US after Congress voted in April to ban it unless the app’s Chinese parent company sells it by Jan 19.

They have sought to have the law struck down, and the Supreme Court has agreed to hear the case. However, if the court does not rule in ByteDance’s favour and no divestment occurs, the app could be effectively banned in the US on Jan 19, one day before Trump takes office.

“This case presents an unprecedented, novel, and difficult tension between free-speech rights on one side, and foreign policy and national security concerns on the other,” Trump said in a filing on Friday.

“Such a stay would vitally grant President Trump the opportunity to pursue a political resolution that could obviate the court’s need to decide these constitutionally significant questions,” the filing added.

Free speech advocates separately told the Supreme Court on Friday that the US law against Chinese-owned TikTok evokes the censorship regimes put in place by the US’s authoritarian enemies.

Trump indicated earlier this week that he favoured allowing TikTok to keep operating in the US for at least a little while, saying he had received billions of views on the social media platform during his presidential campaign.

The justice department has argued that Chinese control of TikTok poses a continuing threat to national security, a position supported by most US lawmakers.

TikTok says the justice department has misstated the social media app’s ties to China, arguing that its content recommendation engine and user data are stored in the US on cloud servers operated by Oracle Corp, while content moderation decisions that affect US users are made in the US as well.