U.S. District Judge Reed O'Connor, who was appointed to the U.S. District Court for the Northern District of Texas by President George W. Bush, sided with conservative plaintiffs who argued that the administration's rule violated religion freedom. In his opinion, first published by Buzzfeed's Chris Geidner, O'Connor argued that the conservatives had shown that the ruling would harm them, and that the administration lacked a basis for its definition of gender identity.

"The government's usage of the term sex in the years since Title IX's enactment bolsters the conclusion that its common meaning in 1972 and 2010 referred to the binary, biological differences between males and females," O'Connor wrote. "Prior to the passage of the ACA in 2010 and for more than forty years after the passage of Title IX in 1972, no federal court or agency had concluded sex should be defined to include gender identity."

As they prepare for a busy 2017 legislative push, congressional Republicans have criticized the Obama administration's flurry of final-year regulations and drafted legislation to undo some of it. It was unclear on Saturday evening how the Obama administration would respond to the injunction, which was O'Connor's second ruling against the administration on gender identity.

While the Affordable Care Act did not include expansive language about gender identity, the administration has, since 2013, issued a series of rulings making it easier for transgender Americans to use government services in accordance with that identity.