Idaho governor Brad Little (R.) on Monday signed the Fairness in Women's Sports Act to prohibit biologically male students from participating in all-female sports.
"Athletic teams or sports designated for females, women, or girls shall not be open to students of the male sex," the bill states.
The law cites differences in male and female physiology that results in distinct athletic capabilities.
"Under this bill, boys and men will not be able to take the place of girls and women in sports because it is not fair," state representative Barbara Ehardt told Reuters.
Female students from Connecticut have filed a federal lawsuit seeking to prevent schools in the state from allowing transgender people to compete in women's sports after the students lost competitions to athletes born male.
Chelsea Mitchell, one of the athletes challenging the state of Connecticut, said she was happy about Idaho's new legislation.
"I have lost four state championships because my state's policy ignores the physical advantages males have over females in sports and allows males to compete in the girls' category," Mitchell told the Daily Wire. "Four times I was the fastest female in my race, but I didn't get the gold medal or the state title; the males in my race took that honor. I have watched this happen over and over again in my sport in Connecticut, as so many girls have been impacted."
The governor also signed a second bill on Monday that prohibits transgender people from changing their sex on their birth certificate.
Sam Brinton, the head of advocacy and government affairs for the pro-trans group the Trevor Project, argued this policy would endanger the lives of transgender youth.
"It is a sad day in the United States when lawmakers are more determined to stop trans young people from playing games than to provide them with the care, support, and opportunities they need to survive and thrive," he said.