The lawsuits, filed in federal courts in Seattle and Baltimore, say the ban issued on Friday violated United States constitutional guarantees of equal protection and due process.
-Josh Block, ACLUTrump's order, signed last Friday, would also bar "the Department of Defense from using its resources to provide medical treatment regimens for transgender individuals now serving in the military", CNN reported.
The brief includes copies of the President's tweets on the issue, including one on July 26 where he wrote: "Our military must be focused on decisive and overwhelming victory and can not be burdened with the tremendous medical costs and disruption that transgender in the military would entail".
It halted years of efforts to eliminate barriers to military service based on sexual orientation or gender identity, including an "Open Service Directive" created to let transgender people serve without fear of discharge.
In late July, Trump first floated the idea for a transgender military ban in a series of tweets that caught many, including military leaders, by surprise. "Men and women who are transgender with the courage and capacity to serve deserve more from their commander in chief".
Both lawsuits discuss the methodic detail with which former Defense Secretary Ashton Carter over the course of one year under the Obama administration examined the issue of transgender service - a process that included commissioning a study by the RAND Corp. that found no drawbacks either to military readiness or medical costs. In a two-and-a-half page order, the president directed Secretary of Defense James Mattis to return to the pre-2016 policy of banning service by men and women who are transgender.
The ACLU says an estimated 8,800 or more transgender people now serve in the military, and asserts that Trump's concerns about military preparedness, unit cohesion and medical costs are baseless.
Trump issued a memorandum on Friday afternoon ordering a reversal of Obama administration rules that had started to let transgender people to serve openly in the military. It notes that 18 other countries, including 11 North Atlantic Treaty Organisation members, allow transgender people to serve openly, and says Rand found no significant effect on operational effectiveness. "The most they can decide are the individual fates of now serving transgender personnel, whose presence will be inconsistent with new military policy".
The ACLU lawsuit is one of at least three brought since the announcement.
Davidson said that move creates ambiguity that also requires an immediate lawsuit.
The National Center for Lesbian Rights and GLBTQ Legal Advocates & Defenders, or GLAD, filed a lawsuit against the ban earlier this month in U.S. District Court for the District of Columbia.