“This is not who we are.”
Advocates have raised concerns that a president can single-handedly decide whether trans people may serve.
Social media users have flooded the hashtag with gay content.
The guide is intended to support homeless shelters in turning away trans women.
The move was announced in the middle of Pride month and on the anniversary of the Pulse massacre.
A lawsuit has been filed over the Trump administration's attempt to scrap discrimination protections.