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 until 12 November, when it could also be fully 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?
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.
Why does the US want the apps banned?
The Trump administration has repeatedly said the apps are a threat because of their collection of data.
Friday’s statement from the commerce department said the governing Chinese Communist Party “has demonstrated the means and motives to use these apps to threaten the national security, foreign policy, and the economy of the US.”
President Trump has repeatedly criticised China since taking office, accusing Beijing of unfair trading practices and intellectual property theft.
ByteDance has denied that it holds any user data in China, saying it is stored in the US and in Singapore. Tencent, which owns WeChat, has said that messages on its app are private.
While TikTok has millions of users in the US, it is not clear how many of WeChat’s billion users are based outside China, although it is likely to be a significant number.
The UK Information Commissioner’s Office, a privacy watchdog, is also currently investigating the app.
Hina Shamsi, director of the American Civil Liberties Union’s National Security Project said the order violated First Amendment rights.
“The order also harms the privacy and security of millions of existing TikTok and WeChat users in the United States by blocking software updates, which can fix vulnerabilities and make the apps more secure,” she said.
“To truly address privacy concerns raised by social media platforms, Congress should enact comprehensive surveillance reform and strong consumer data privacy legislation.”
What are the apps?
TikTok is a video-sharing app. Users can post up to a minute of video and have access to a huge database of songs and filters.
It collects a huge amount of user data – including what videos people watch and comment on, location data, phone model and even how people type. But much of this data collection is similar to other social networks like Facebook.
In September the company said it had more than 100 million users. It is thought to have more than 800 million members around the world.
WeChat was set up in 2011. It is a multi-purpose app allowing users to send messages, make mobile payments and use local services. It has been described as an “app for everything” in China and has more than one billion monthly users.
But WeChat insists encryption means others cannot “snoop” on your messages, and that content such as text, audio and images are not stored on its servers – and are deleted once all intended recipients have read them.