(CNN) A federal judge says transgender women and girls in Idaho cannot be banned from sports teams corresponding to their gender, blocking an Idaho law that attempted to do so.
"This is a victory for all women and girls in Idaho. Trans people belong in sports," wrote the American Civil Liberties Union, which provided legal representation in the case.
Gov. Brad Little signed the "Fairness in Women's Sports Act" in March, which would not allow athletes to participate on a women's team without first verifying that person's "internal and external reproductive anatomy" if her sex is disputed. But Judge David Nye granted a motion for a preliminary injunction against the act Monday.
CNN has reached out to Little's office for comment.
From South Dakota to Tennessee to Connecticut, transgender athletes in recent years have fought against legislation aimed at limiting their participation due to their gender identity. Many argue such policies violate Title IX, the federal anti-discrimination law in education credited with leveling the playing field for women in sports.
Nye said Idaho did not provide sufficient reasons for the law to exist.
"The State has not identified a legitimate interest served by the Act that the preexisting rules in Idaho did not already address, other than an invalid interest of excluding transgender women and girls from women's sports entirely, regardless of their physiological characteristics," Nye wrote.
The law was challenged by transgender cross-country athlete Lindsay Hecox, a student at Boise State University.
A second plaintiff in the case is a 17-year-old cisgender athlete -- unnamed in the lawsuit because she is a minor -- who is concerned that she may be forced to invasively "prove" her gender because of her athletic build and "masculine" personal traits.
Judge Nye agreed that was unfair and "being subject to a sex dispute is itself humiliating." The law does not have a similar requirement for male athletes, Nye noted.
The preliminary injunction is not the final say in the lawsuit, but Nye said in his 87-page order "plaintiffs are likely to succeed in establishing the Act is unconstitutional."