A Toronto-based transgender former member of the U.S. Navy and Marines says Donald Trump doesn’t understand the meaning of the acronym “LGBT,” following his Twitter announcement that trans people will not be allowed to serve in the military.

“His lack of understanding is seriously harmful,” military vet and activist Rachel Lauren Clark told CTV News Channel on Thursday. “I think that he doesn’t understand that the ‘T’ in ‘LGBT community’ stands for trans people. I think he just thinks that everyone is gay and lesbian.”

Clark is among the many members of the LGBT community who are condemning Trump’s decision to ban transgender people from military service “in any capacity,” in a move he announced on Twitter Wednesday morning. Trump’s decision came just over a year after he voiced strong support for the LGBT community, tweeting: “I will fight for you while Hillary brings in more people that will threaten your freedoms.”

In addition to condemning Trump’s decision, Clark harshly criticized the president for announcing the policy via social media, without providing further guidance to his own staff who have been unable to offer details on the rollout.

“I don’t think anyone should hear about their job on Twitter,” Clark said, calling it a “very unprofessional thing” to do on the president’s part. “What do you do when you go to work the next day and you don’t know what the president means when he tweets these things?”

Clark points out that the U.S. military employs nearly 2,500 trans people, and has been a viable career option for many who otherwise have had difficulty finding work. “This has a devastating effect on our community,” she said.

The White House has not released full details on when or how the president’s tweets might be enforced.