President Donald Trump on Friday officially issued a ban on transgender people serving in the military, and now, the American Civil Liberties Union (ACLU) is taking him to court.

The organization joins the National Center for Lesbian Rights (NCLR) and GLBTQ Legal Advocates & Defenders (GLAD), who jointed filed a similar lawsuit earlier in August on behalf of five transgender service members.

Trump first announced the ban through Twitter in late July.

The ACLU announced Monday morning that it would challenge the directive in court, arguing that it violates "the constitutional guarantees of equal protection and substantive due process by singling out transgender individuals for unequal and discriminatory treatment," according to a press release.

It continues, "The lawsuit argues that the ban discriminates based on sex and transgender status and that the ban is based on uninformed speculation, myths and stereotypes, moral disapproval, and a bare desire to harm this already vulnerable group."

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The directive not only bans transgender individuals from serving in the military, but it also gives Defense Secretary Jim Mattis the ability to kick out transgender soldiers currently serving, and it directs the military to halt paying for gender confirmation surgery. The military can, however, continue to pay for the surgery for current members if it would put the health of individuals in transition in danger.

Online, people celebrated the ACLU's announcement.

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Mattis has to put the policy into place within six months, according to The New York Times.

When he first tweeted about the ban, Trump cited funding as the reason behind the policy, but that was quickly debunked, as data shows the military spends a small amount of money on gender confirmation surgeries. It even shows that Viagra costs the military five times more.

"Each and every claim made by President Trump to justify this ban can be easily debunked by the conclusions drawn from the Department of Defense’s own review process," said Josh Block, senior staff attorney with the ACLU’s LGBT & HIV Project.

The initial news came as a shock, not only in the way it was presented, but also because the Obama administration only recently rolled back a ban on transgender individuals serving in the military in 2016.

At the time of Trump's Twitter announcement, he received sharp criticism, especially from Democrats and others such as Chelsea Manning and former Defense Secretary Ash Carter.