It said the Chinese-owned messaging service is a threat to national security.
Last week, the US Commerce Department moved to ban WeChat from app stores.
On Saturday, Magistrate Judge Laurel Beeler in California agreed to delay US restrictions, saying they would affect users’ First Amendment rights.
In a filing on Friday, the Justice Department asked Ms Beeler to allow for an immediate ban while the case works its way through court.
WeChat is a messaging-focused app popular with many Chinese-speaking Americans that serves as a lifeline to friends, family, customers and business contacts in China.
It is owned by Chinese tech giant Tencent.
The Justice Department claims WeChat allows the Chinese government to collect and use personal data on Americans to advance its own interests.
The filing states WeChat has approximately 19 million active daily users in the US in a range of formats including text, images, video and audio.
The Justice Department argues the US will suffer irreparable harm, both substantive and procedural, if the court does not stay its decision.
The Trump administration has targeted WeChat and another Chinese-owned app, TikTok, for national security and data privacy concerns, in the latest flashpoint amid rising tensions between Washington and Beijing.
