President Trump has signed a memorandum that directs the U.S. military not to accept transgender men and women as recruits and halts the use of government funds for sex-reassignment surgeries for active personnel unless the process is already underway. (CBS via Reutes)

The American Civil Liberties Union filed a lawsuit Monday challenging the Trump administration’s controversial ban on transgender people enlisting, receiving Armed Forces medical care for sex-reassignment surgeries, and possibly continuing to serve.

The suit, filed in federal court in Maryland on behalf of six active-duty military members, argues that the ban is unconstitutional because it discriminates against transgender people.

“It’s such an egregious attempt to target transgender individuals who have devoted their careers and lives to the United States,” said Chase Strangio, a staff attorney for the ACLU. “The president claims in tweets transgender service costs money and military readiness. The reality is the Department of Defense concluded after years of study that is baseless.”

A Defense Department spokesman said the Pentagon was aware of the lawsuit, but referred questions to the Justice Department.

“We are examining the claims in this lawsuit and conferring within the Government,” the Justice Department wrote in a statement.

President Trump spoke about banning transgender people from the military in Bedminster N.J. on Aug. 10. (The Washington Post)

The lawsuit was filed days after Trump formally ordered the Pentagon to ban the recruitment of openly transgender people and to determine whether those already serving should be allowed to remain. It is at least the third civil suit challenging Trump’s transgender military ban.

In late July, Trump first floated his plan for a transgender military ban in a series of tweets that caught many, including military leaders, by surprise.

“After consultation with my Generals and military experts, please be advised that the United States Government will not accept or allow Transgender individuals to serve in any capacity in the U.S. Military,” Trump wrote in the tweets. “Our military must be focused on decisive and overwhelming victory and cannot be burdened with the tremendous medical costs and disruption that transgender in the military would entail.”

The decision was cheered by many religious conservatives but angered LGBT activists, liberals and some in Trump’s own party, such as Sen. John McCain (R-Ariz.), who complained about the president rolling out a major policy on Twitter and possibly forcing people out of the military who were otherwise qualified.

The ban reversed an Obama administration decision to allow transgender people to serve openly. The armed forces were set to begin enlisting transgender people July 1, but Defense Secretary Jim Mattis delayed that move, citing a need for more study.

Before the policy change by the Obama administration, the Pentagon had concluded that there was no basis for the military to exclude transgender people, as long as they could meet the same fitness requirements as other service members. The review examined medical care, military readiness and other factors.

There is no official tally of transgender military members, and estimates vary widely. One recent study by the Rand Corp. put the number on active duty at about 2,500, while another from the Williams Institute at UCLA Law School estimated that there were 15,500 on active duty, in the National Guard and in the reserves.

The six active-duty military personnel who are plaintiffs in the lawsuit are Navy Petty Officer 1st Class Brock Stone, an anonymous Air Force senior airman, Airman 1st Class Seven Ero George, Navy Petty Officer 1st Class Teagan Gilbert, Army Staff Sgt. Kate Cole, and Marine Corps Technical Sgt. Tommie Parker.

Stone, 34, who is the lead plaintiff and is based at Fort Meade in Maryland, has served in the Navy for 11 years, including a nine-month deployment to Afghanistan, according to the lawsuit. Stone has been receiving treatment at Walter Reed National Military Medical Center and is expected to undergo surgery related to sex reassignment in 2018, according to the lawsuit.

None of the plaintiffs were available for comment.