TikTok and WeChat will be banned from US app stores from Sunday, unless President Donald Trump agrees to a last-minute deal.
The Department of Commerce said it would bar people in the US from downloading the messaging and video-sharing apps through any app store on any platform.
The Trump administration says the companies threaten national security and could pass user data to China.
But China and both companies deny this.
WeChat will effectively shut down in the US on Sunday, but people will still be able to use TikTok as normal until 12 November, when it could also be fully banned.
If a planned partnership between Oracle and TikTok owner ByteDance is agreed and approved by President Trump, the app would not be banned.
It is not yet clear whether Mr Trump will approve the deal, but he is expected to review it before the Sunday deadline.
What does the order say?
“At the president’s direction, we have taken significant action to combat China’s malicious collection of American citizens’ personal data,” the US Department of Commerce Secretary Wilbur Ross said in a statement.
The department acknowledged that the threats posed by WeChat and TikTok were not identical but said that each collected “vast swathes of data from users, including network activity, location data, and browsing and search histories”.
While WeChat closes on Sunday, TikTok users will still be able to use their app virtually as normal, although they will not be able to download new updates.
“The President has provided until November 12 for the national security concerns posed by TikTok to be resolved,” the commerce department said.