JEWEL SAMAD via Getty Images Protesters display placards against President Donald Trump during a demonstration in front of the U.S. Army career center in New York City's Times Square on July 26, 2017.

On Monday, the U.S. military is set to formally allow transgender citizens to sign up for service ― a historic move likely to rile President Donald Trump.

Federal courts have said that trans citizens can be accepted into the armed forces, and the Defense Department has already issued policy guidelines concerning their recruitment. But Trump could seek a last-minute Supreme Court intervention to stop the process.

“It definitely seems like they aren’t going to the Supreme Court, but until we say ‘Happy New Year’ on Sunday night I’m not taking anything for granted,” Joshua Block, a lawyer with the American Civil Liberties Union, told Reuters.

In July, Trump announced his intention to ban trans people from serving in the military. He claimed that transgender troops “burden” the armed services with “tremendous medical costs.” In fact, this is not true.

Last week, two U.S. appeals courts refused an emergency request from the Trump administration to lift lower court orders that would allow the enlistment ban to continue after Jan. 1.

Elijah Sellers, a trans soldier currently serving on the Navy’s USS Bataan, told HuffPost in October that he was “terrified” by Trump’s evident desire to rid the military of its transgender troops.

“In the military, we judge people based off of their work ethic and their ability to get a job done and do it correctly and I feel like that’s the most important thing,” Sellers said. “And on the street, nobody would know I was transgender. So I really don’t think it’s as big of an issue as some people think it is.”