WASHINGTON — In a blow to President Donald Trump, the Supreme Court on Wednesday said his administration cannot enforce a new policy that restricts treatment for transgender inmates in federal prison.

The justices in a brief order rejected an emergency application filed by the administration that sought to block a lower court injunction against the proposal. The court order included no explanation, saying only that two conservative justices, Clarence Thomas and Samuel Alito, would have granted it.

There are about 1,000 transgender inmates in federal custody.

“This is a critical ruling for our clients and all transgender people in Bureau of Prisons custody,” Li Nowlin-Sohl, a lawyer with the American Civil Liberties Union representing the plaintiffs, said in a statement.

“The denial of medically necessary health care, including gender-affirming health care, to people in prison is a violation of their fundamental constitutional rights,” she added.

The policy, which will continue to be litigated over in…