A federal appeals court on Friday declined to temporarily block a ban on TikTok, setting the stage for a Supreme Court showdown over whether the law should take effect while the social media platform challenges it. Last week, the D.C. Circuit Court of Appeals unanimously upheld the law, clearing the way for it to take effect on January 19. Days later, TikTok asked a court to temporarily halt the ban while the company asked the Supreme Court to review its challenge to the law. The appeals court unanimously rejected the request in a brief, unsigned order, calling the ban "unjustified."

The TikTok ban is one of the most closely watched pieces of federal legislation in recent years, and the law is widely expected to eventually make its way to the conservative-majority Supreme Court.

By law, the platform must be sold to new non-Chinese owners or it will be banned in the United States. After the January deadline, U.S. app stores and internet services could face hefty fines for hosting TikTok if it is not sold. (By law, the president can extend the deadline on a one-time basis).

The company said in court papers that if the appeals court denies interim relief, it will ask the Supreme Court to urgently intervene to temporarily block the law. This request may be made at any time.

Lawyers for the company had argued to the appeals court that refusing to temporarily block the law would force the Supreme Court to review the matter "in just a few weeks, and over the holidays," on what it called its "shadow docket."

"Out of respect for the important role of the Supreme Court, this court should issue a temporary injunction to make the review process more prudent and orderly," they wrote in court documents.

The Biden administration, meanwhile, has urged an appeals court not to issue a temporary injunction against the law, arguing that doing so could make the company wait months before appealing to the Supreme Court, effectively halting enforcement of the law indefinitely.

The U.S. Congress passed the ban with bipartisan support earlier this year, and President Joe Biden signed it into law in April. The ban comes in response to years of concern in Washington that the app's Chinese parent company, ByteDance, posed a threat to national security.

In a ruling last week, the D.C. Circuit said the law did not violate the U.S. Constitution and held that it met the legal standard of strict scrutiny that government restrictions on speech must meet to be valid.

"The law is the culmination of extensive bipartisan action by Congress and successive presidents. The law was carefully crafted to target only the control of foreign adversaries as part of a broader effort to address the well-documented national security threat posed by the (People's Republic of China)," the ruling said. "Under the circumstances, the provisions of the bill before us withstand the strictest scrutiny."

However, TikTok's lawyers said that given the sensitivity of the legal issues at the center of the case, the Supreme Court should have the final say on the matter.

"The court's finding that the bill meets the requirements of strict scrutiny will certainly attract the attention of the Supreme Court," they wrote in court filings. "Whether the bill is, at the very least, one of those rare cases of law that withstands strict scrutiny is an open question."

ByteDance has stated that it will not sell TikTok.

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