WeChat users who sued President Donald Trump seeking to block his executive order banning the Chinese messaging app in the U.S. on national security grounds asked to see the evidence supporting his decision.

The U.S. WeChat Users Alliance, which filed suit last month in federal court in San Francisco, on Thursday asked the judge to order the government to turn over the evidence on an expedited basis so that they can use it in their bid for a preliminary injunction. The U.S. is opposing the evidence request.

A hearing is scheduled for Sept. 17 on the users’ request for a preliminary injunction. Trump’s order is due to go into effect Sept. 20 when the U.S. Commerce Department is expected to delineate exactly what transactions with the app, owned by Shenzhen, China-based Tencent Holdings Ltd., are prohibited.

The U.S. is arguing the group is not entitled to any evidence because the executive order has no legal effect on them and courts can’t review national security determinations by the president. Only the Commerce Department’s implementation of the order may be challenged, the government maintains.

According to the group, Trump’s Aug. 6 order would sunder the primary and often exclusive channel many U.S. residents use to communicate with family and friends in both China and the United States. WeChat is also used to run businesses and non-profit organizations, practice religion and as a source news. The suit claims WeChat is so integral to Chinese and Chinese Americans’ lives that a ban would be like “losing a limb” for some users.

The case is U.S. WeChat Users Alliance v. Trump, 20-CV-05910, U.S. District Court, Northern District of California (San Francisco).