“As members of Congress with an abiding interest in our nation’s military and its policies towards the LGBTQ community, we write to not only express our strong opposition to President Trump’s recent tweets seeking to ban transgender individuals from the military, but to remind you not to comply with any unconstitutional directive which may ultimately be issued,” the 53 lawmakers wrote to Defense Secretary James Mattis and Chairman of the Joint Chiefs of Staff Gen. Joseph Dunford in a letter Friday.

The letter was organized by the top Democrats on the House Armed Services and Judiciary committees, Reps. Adam Smith (Wash.) and John Conyers Jr. (Mich.), respectively. Signatories hail from those committees, as well as the Congressional LGBT Equality Caucus.