By Andrew Chung and David Shepardson

WASHINGTON (Reuters) - TikTok made a last-ditch effort on Monday to continue operating in the United States, asking the Supreme Court to temporarily block a law intended to force ByteDance, its China-based parent company, to divest the short-video app by Jan. 19 or face a ban.

TikTok and ByteDance filed an emergency request to the justices for an injunction to halt the looming ban on the social media app used by about 170 million Americans while they appeal a lower court's ruling that upheld the law.

Congress passed the law in April amid national security concerns. The Justice Department has said that as a Chinese company, TikTok poses "a national-security threat of immense depth and scale" because of its access to vast amounts of data on American users, from locations to private messages, and its ability to secretly manipulate content that Americans view on the app.

The U.S. Court of Appeals for the District of Columbia Circuit in Washington on Dec. 6 rejected arguments by the companies and some TikTok users that the law violates their free speech rights under the U.S. Constitution's First Amendment. Free speech advocates, including the American Civil Liberties Union, criticized the D.C. Circuit's ruling.

The D.C. Circuit on Dec. 13 denied an emergency request by TikTok and ByteDance to temporarily halt the law.

Without an injunction, the ban on TikTok would make the company far less valuable to ByteDance and its investors, and hurt businesses that depend...