LGBT groups expressed outrage Friday after President Trump carried through on his Twitter promise to ban transgender people from the military by issuing an official directive.

“The president’s order to remove transgender service members from the United States armed forces and deny them healthcare is nothing less than a purge,” OutServe-SLDN Executive Director Matt Thorn said in a statement Friday.

“He is implementing this purge based on bigotry, motivated by agents of an ideology that has no concern for the national defense, and in blatant disregard of the experience of career officers who spent more than a year developing and implementing the current policy.”

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Late Friday afternoon, the White House announced that Trump signed a presidential memo that prohibits the military from enlisting transgender people and from using funds to pay for gender transition-related surgery.

For currently serving transgender troops, 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 has six months to determine what to do with them.

The memo serves as Trump’s fulfillment of a ban he announced on Twitter. In late July, he tweeted that the military “will not accept or allow transgender individuals to serve in any capacity.”

“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. Thank you,” he continued.

Despite the tweets, the Pentagon said it would not change its policy until something official — such as Friday’s memo — came from the White House.

OutServe threatened to sue immediately after Trump’s tweet, but held off until an official policy was unveiled.

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On Friday, the group said it and prominent LGBT legal group Lambda Legal would file suit “swiftly.”

“We recognize this purge for what it is — a discriminatory attack on the people who have volunteered their lives for the defense of the country,” Thorn said in the statement. “It is arbitrary and capricious, a callous and questionable exercise of constitutional authority which is beneath the dignity of a Commander-in-Chief.”

Lambda Legal, too, promised quick action.

“Hey @realDonaldTrump, expect to get to know us even better VERY soon. See you in court,” Lambda Legal tweeted.

Hey @realDonaldTrump, expect to get to know us even better VERY soon. See you in court. https://t.co/Cxpd6LaHmF — Lambda Legal (@LambdaLegal) August 25, 2017

The National Center for Lesbian Rights (NCLR) and GLBTQ Legal Advocates and Defenders (GLAD) have already filed a lawsuit on behalf of five currently serving transgender troops based on the tweeted ban.

On Friday, NCLR and GLAD called the ban “senseless” and “shameful.”

“This is a senseless and unprecedented attack on dedicated service members who have played by the rules,” Shannon Minter, NCLR legal director, said in a statement. “Our military already has standards and systems in place to ensure our troops are qualified and fit to serve. Trump's ban is about politics, not military policy, and it will make our country less secure.”

“This policy is a shameful slap in the face to people who put their lives on the line everyday to defend our country," said Jennifer Levi, GLAD transgender rights project director. "We are moving quickly with our plaintiffs to see that a court puts a stop to this latest demonstration of President Trump playing politics with people’s lives.”

The American Military Partner Association (AMPA), meanwhile, called the ban “horrifying” and called on Congress to take action to stop it.

“This horrifying, vicious assault on thousands of actively serving troops has turned from reckless tweets into an unabashedly discriminatory policy aiming to purge the military of thousands of transgender men and women," AMPA President Ashley Broadway-Mack said in a statement.

"We unequivocally condemn this ban as an unpatriotic attack on currently serving troops and qualified transgender recruits who want to serve their country. It is imperative that Congress immediately takes action or a judge issues an injunction stopping this unprecedented assault from moving forward."