SAN FRANCISCO • A group of WeChat users has asked a federal judge to block the Trump administration from imposing a ban on what they say appears to be all uses of the Chinese messaging app in the United States over national security concerns.

In a complaint filed in federal court in San Francisco on Friday, Chinese-American lawyers who formed the US WeChat Users Alliance are claiming that President Donald Trump's planned restriction on the app is unconstitutional.

His Aug 6 order bans Americans from carrying out transactions with WeChat and TikTok, another popular Chinese social media platform, as of the middle of next month.

The "vaguely worded" executive order does not define what transactions will be prohibited, the lawyers said.

It also leaves people and firms at a loss of whether they will violate the order if they do not fundamentally change the way they communicate or run their businesses, the lawyers added.

They linked Mr Trump's order with his recent comments that have been critical of China, including blaming the country for the coronavirus pandemic.

"Neither the executive order itself nor the White House provided concrete evidence to support the contention that using WeChat in the United States compromises national security," the group said in the complaint. They claim that Mr Trump's order violates WeChat users' free speech and due process rights because it does not provide notice of the specific conduct that is prohibited.

WeChat - which was developed by Tencent Holdings-is used by millions of Americans and US residents to communicate with people whose first language is Chinese, according to the alliance.

BLOOMBERG