The Trump administration on Tuesday took a major step to bar transgender troops from the U.S. military, kick-starting a constitutionally dubious "purge" with a new set of rules sure to continue its drawn out battle over the policy in federal courts.

"The Trump administration is built on demonizing minority groups; reversing the civil rights gains of immigrants, people of color, women, and the LGBTQ movement will forever remain the hallmarks of their time in office."
—Harper Jean Tobin, NCTE

"The start of this looming purge represents an unprecedented step backward in the social and civil progress of our country and our military," Harper Jean Tobin, director of policy for the National Center for Transgender Equality (NCTE), said in a statement.

President Donald Trump initially announced a ban on trans troops with a series of tweets in 2017—signaling his intention to reverse a policy implemented under former President Barack Obama in 2016 that was praised by much of the LGBTQ community.

Trump's attempts to expel trans people from service and block them from enlisting sparked legal challenges, but in January, the U.S. Supreme Court's right-wing majority gave the green light for the administration to pursue its "bigoted" and "cruel" effort while fights in court continue.

"The Trump administration is built on demonizing minority groups; reversing the civil rights gains of immigrants, people of color, women, and the LGBTQ movement will forever remain the hallmarks of their time in office," Tobin said, calling on Congress to block the policy.

Aaron Belkin is the director of the Palm Center, a think tank that has conducted research on trans people serving in the military. With these rules, he said, "the Trump administration has chosen prejudice and politics over the truth of open service as revealed by the testimonies of dozens of medical and military leaders and the service and sacrifice of 14,700 transgender service members."

Despite ongoing litigation, the second-in-command at the Defense Department signed off on a memo (pdf) detailing the administration's official rules. As of April 12, transgender service members and new applicants only can serve under their "biological sex," effectively forcing them to conceal their gender identity or leave the military.

New applicants with gender dysphoria—a medical diagnosis for someone who experiences distress tied to the difference between the gender they were assigned at birth and the gender they believe themselves to be—are "presumptively disqualified" (pdf), as are those with a history of medical transition treatment—specifically, cross-sex hormone therapy or sex reassignment surgery.

Current service members who joined the military in their preferred gender or are diagnosed with gender dysphoria before the Trump administration's policy takes effect are exempt from the new rules. Under the Pentagon's policy, waivers may be granted on a case-by-case basis.

"In addition to being unlawful, moving forward with this ban is also deeply immoral and deeply insulting to the many transgender troops who are bravely serving their country."
—Jennifer Levi, GLAD

GLBTQ Legal Advocates & Defenders (GLAD) and the National Center for Lesbian Rights (NCLR) are among the groups who have taken the administration to court over the trans troop ban and other anti-LGBTQ policies.

"With brazen disregard for the judicial process, the Pentagon is prematurely and illegally rolling out a plan to implement the ban when a court injunction remains in place prohibiting them from doing so," noted Jennifer Levi, GLAD's Transgender Rights Project director. "In addition to being unlawful, moving forward with this ban is also deeply immoral and deeply insulting to the many transgender troops who are bravely serving their country."

NCLR legal director Shannon Minter vowed to "continue our fight in the courts until the ban is permanently blocked," but also called on Congress to take swift action and urged "everyone who cares about the integrity of our military and the well-being of our troops to contact your representatives and tell them to support this legislation."

This post has been updated with a link to the Pentagon memo and details from the directive.