The federal lawsuit was filed in Maryland on Monday by the ACLU of Maryland on behalf of several service members who are transgender.
Trump directed the Pentagon on Friday to implement the ban on transgender individuals joining the military, which he first announced in a tweet. He also gave to the Pentagon the authority to decide the future of openly transgender people already serving.
The lawsuit says Trump's policy violates the equal protection rights of transgender service members who now have "grave reason to fear for their careers."