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.
TikTok said it was "disappointed" in the order and disagreed with the commerce department, saying it had already committed to "unprecedented levels of additional transparency" in light of the Trump administration's concerns.
"We will continue to challenge the unjust executive order, which was enacted without due process and threatens to deprive the American people and small businesses across the US of a significant platform for both a voice and livelihoods."
The ban order from the Department of Commerce follows President Trump's executive orders signed in August. It gave US businesses 45 days to stop working with either Chinese company.
If a planned partnership between US tech firm Oracle and TikTok owner ByteDance is agreed and approved by President Trump, the app will 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.