Donald Trump has signed an executive order banning any US transactions with the Chinese company that owns the video-sharing app TikTok.
The order, which will come into effect in 45 days, comes after his administration warned it was stepping up efforts to purge "untrusted" Chinese apps.
Tencent, which owns the WeChat app, is also being targeted with similar measures.
TikTok responded by suggesting it could sue the US Government over the "dangerous precedent" the order will set for "the concept of free expression and open markets".
The app is hugely popular among young people in the US and elsewhere - and ByteDance operates a separate version of the app for the US market. WeChat is a messaging app that's widely used by Chinese expats who want to keep in touch with friends and family back home.
These executive orders have been vaguely worded - but it is possible that Apple and Google may be banned from hosting these apps on their stores.
Mr Trump's administration has described TikTok and WeChat as "significant threats" - claiming that TikTok in particular may be used for disinformation campaigns that benefit the Chinese Communist Party.
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The president said that the US "must take aggressive action against the owners of TikTok to prevent our national security".
Earlier this week, Mr Trump said that he would support the sale of TikTok's US operations to Microsoft as long as the US government got a "substantial proportion" of the sale price.
The new executive order alleges: "TikTok, a video-sharing mobile application owned by the Chinese company ByteDance Ltd, has reportedly been downloaded over 175 million times in the US and over one billion times globally.
"TikTok automatically captures vast swaths of information from its users, including Internet and other network activity information such as location data and browsing and search histories.
"This data collection threatens to allow the Chinese Communist Party access to Americans' personal and proprietary information."
Both TikTok and WeChat say they do not share data with the Chinese government.
In a statement, TikTok expressed shock at the executive order, saying it relied on "unnamed 'reports' with no citations, fears the app 'may be' used for misinformation campaigns with no substantiation of such fears and concerns about the collection of data that is industry standard for thousands of mobile apps around the world."
It warned the order risks undermining global businesses' trust in the US.
"We will pursue all remedies available to us in order to ensure that the rule of law is not discarded and that our company and our users are treated fairly - if not by the Administration, then by the US courts," it read.