President Trump Donald John TrumpBubba Wallace to be driver of Michael Jordan, Denny Hamlin NASCAR team Graham: GOP will confirm Trump's Supreme Court nominee before the election Southwest Airlines, unions call for six-month extension of government aid MORE is moving ahead with his plan to ban most transgender people from serving in the military, with limited exceptions, following up on a proposal he called for last summer.

The White House issued a memorandum late Friday on policies determined by Defense Secretary James Mattis James Norman MattisBiden courts veterans amid fallout from Trump military controversies Trump says he wanted to take out Syria's Assad but Mattis opposed it Gary Cohn: 'I haven't made up my mind' on vote for president in November MORE, stating that transgender people are "disqualified from military service except under limited circumstances."

The memo, filed in U.S. District Court in Seattle, states that "transgender persons with a history or diagnosis of gender dysphoria -- individuals who the policies state may require substantial medical treatment, including medications and surgery -- are disqualified from military service except under certain limited circumstances."

Mattis will have some leeway in implementing the policy, the memo states, as will Homeland Security Secretary Kirstjen Nielsen Kirstjen Michele NielsenDHS IG won't investigate after watchdog said Wolf, Cuccinelli appointments violated law Appeals court sides with Trump over drawdown of immigrant protections Democrats smell blood with new DHS whistleblower complaint MORE when it comes to the Coast Guard. The ban is something Mattis "concluded should be adopted," it notes.

White House press secretary Sarah Huckabee Sanders issued a statement saying that the decision to implement the ban came after "extensive study by senior uniformed and civilian leaders, including combat veterans."

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"This new policy will enable the military to apply well-established mental and physical health standards—including those regarding the use of medical drugs—equally to all individuals who want to join and fight for the best military force the world has ever seen," Sanders said.

LGBT advocates quickly denounced the move, which they say is expected to be constrained by existing court orders unless there is further court action.

"There is simply no way to spin it, the Trump-Pence Administration is going all in on its discriminatory, unconstitutional and despicable ban on transgender troops,” Human Rights Campaign President Chad Griffin said in a statement.

“The Trump-Pence administration’s continued insistence on targeting our military families for discrimination is appalling, reckless, and unpatriotic," added American Military Partner Association President Ashley Broadway-Mack.

The Palm Center, a group that promotes the study of LGBT people in the military, accused the Pentagon of having "distorted the science on transgender health to prop up irrational and legally untenable discrimination that will erode military readiness."

"There is no evidence to support a policy that bars from military service patriotic Americans who are medically fit and able to deploy. Our troops and our nation deserve better," the group said.

Trump first called for a ban on transgender troops in a series of tweets last summer, and followed up in August by issuing a memo banning transgender people from enlisting.

The ban has since been battled over in court, with Mattis in February giving Trump a final recommendation. It was expected that he would recommend Trump allow transgender troops to remain in the military.

A Pentagon spokesman declined to comment on Mattis's recommendation in February, only confirming that the Defense chief had advised the president on the subject.

In a court filing to dissolve an injunction, however, Mattis's unclassified memo to the president states that the Defense Department concluded there were "substantial risks associated with allowing the accession and retention of individuals with a history or diagnosis of gender dysphoria and require, or have already undertaken, a course of treatment to change their gender."

Mattis went on to say that exempting transgender individuals from mental fitness tests undergone by other service members would have a negative effect on overall troop readiness.

"Furthermore, the Department also finds that exempting such persons from well-established mental health, physical health, and sex-based standards, which apply to all Service members, including transgender Service members without gender dysphoria, could undermine readiness, disrupt unit cohesion, and impose an unreasonable burden on the military that is not conducive to military effectiveness and lethality," Mattis wrote.

Several federal courts blocked Trump's initial ban, with one ruling in November that the military would be forced to resume accepting transgender recruits starting this year.

In February, the Pentagon confirmed that one transgender recruit had joined a branch of the military after the ban was lifted due to the court order. That individual passed all tests including medical, officials said.

While the exact number of transgender individuals in active duty service is unknown, a 2016 Rand Corporation study commissioned by the Pentagon estimated the number to be anywhere from 1,320 and 6,630, with 830 to 4,160 others serving in the reserves.

Updated: 10:33 p.m.