TikTok and its Chinese parent company ByteDance are making a fresh legal attempt to stop the impending end of the popular app in the United States.
In a lawsuit filed on Friday night against U.S. President Donald Trump and the Department of Commerce, they are demanding, among other things, an injunction.
A separate suit, to stop a ban on the Chinese app WeChat, was to be heard in a California court on Saturday.
According to decisions by the Washington government, U.S. smartphone users will no longer be able to download TikTok from Monday, and the app will stop working completely on Nov. 12. TikTok has around 100 million users in the U.S.
Trump has dubbed TikTok a security risk on the grounds that Chinese authorities could get data from U.S. users. TikTok and ByteDance deny the allegations.
Trump had issued an executive order in August that would ban TikTok in the United States from the middle of this month unless it was sold to a U.S. company.
The U.S. government is immediately pulling the plug on the Chinese messaging app WeChat because of similar criticisms: It will both disappear from app stores and lose most of its functions on Monday.
WeChat also wants to prevent that in a court in California.
TikTok and ByteDance argue in their lawsuit that the Trump administration's ban violates their rights and the U.S. Constitution. They had already sued over Trump's previous order with similar justification.
At the same time, negotiations about a deal for the US business of the TikTok app are continuing in the background. Trump insists that US investors must have a majority share in TikTok in the U.S.
The Chinese government had torpedoed earlier talks about a purchase of the U.S. business by Microsoft with new export rules for software.
China on Saturday condemned Washington's measures against TikTok and WeChat.
In response to a reporter's question, a spokesperson for China's Ministry of Commerce said the move "seriously damages the lawful rights of the companies involved (and) disrupts the normal order of the market."
The spokesperson said the U.S. aimed to "hunt and suppress" the firms "without evidence" and urged Washington to "reject bullying behavior and immediately halt their wrongdoing," warning that Beijing will otherwise respond with "necessary measures" to protect Chinese interests.
In a statement released on Saturday, WeChat's parent company Tencent said it had "put forward a comprehensive proposal to address" the U.S. government's concerns, and said it "will continue to discuss with the government and other stakeholders in the U.S. ways to achieve a long-term solution."