President Donald Trump has told US firms they have 45 days to stop doing business with TikTok and WeChat, claiming the Chinese apps are a threat to national security.
Mr Trump signed two executive orders targeting two of China’s biggest apps.
It is a major escalation in Washington’s stand-off with Beijing over its power in global technology.
The announcement comes as Microsoft is in talks to buy TikTok ahead of a 15 September deadline set by Mr Trump.
The executive orders against the short-video sharing platform TikTok – owned by Chinese firm ByteDance – and the messaging service WeChat – owned by the Tencent conglomerate is the latest measure in an increasingly broad Trump administration campaign against China.
Mr Trump’s orders are likely to be liable to legal challenges, analysts say.
Earlier on Thursday, Washington announced recommendations that Chinese firms listed on US stock markets should be delisted unless they provided regulators with access to their audited accounts.
What did Trump say?
In both executive orders, Mr Trump says he has found “additional steps must be taken to deal with the national emergency with respect to the information and communications technology and services supply chain”.
He adds: “The spread in the United States of mobile applications developed and owned by companies in the People’s Republic of China (China) continues to threaten the national security, foreign policy, and economy of the United States.”
He refers to both apps as a “threat”. Both orders say any unspecified “transactions” with the apps’ Chinese owners or their subsidiaries will be “prohibited”.
The orders cite legal authority from the National Emergencies Act and the International Emergency Economic Powers Act.
Mr Trump’s executive order claims TikTok’s data collection could allow China to track US government employees and gather personal information for blackmail, or to carry out corporate espionage.
He notes that reports indicate TikTok censors content deemed politically sensitive, such as protests in Hong Kong and Beijing’s treatment of the Uighurs, a Muslim minority.
The US president says the Department of Homeland Security, the Transportation Security Administration (which oversees US airport screening) and the US Armed Forces have already banned TikTok on government phones.
ByteDance and Tencent have declined so far to comment.