The body that regulates amateur and Olympic-style boxing in America, USA Boxing, says it will begin allowing biological male adults who identify as women to compete in the women’s category beginning Monday, the first day of 2024.

In a draft of its new rule book released late Friday, the federation announced that biological females who have transitioned to men also will be allowed to compete against men should they so choose. It said the new rules are based on guidance from the International Olympic Committee’s 2021 Framework on Fairness, Inclusion, and Non-Discrimination on the Basis of Gender Identity and Sex Variations that left decisions about transgender athletes up to each nation’s federation.

“Since boxing’s (international federation) has not determined transgender eligibility and boxing is considered a combat sport, USA Boxing’s overriding objective is the safety of all boxers and fair competition between all boxers,” the organization said in the new rule book.

Boxers under the age of 18 still will be required to compete based on their sex at birth. Those who have transitioned as adults, however, and met a number of restrictions will be able to choose their class themselves.

Among the requirements is that male-to-female transgender athletes must have completed gender reassignment surgery and four years of quarterly hormone testing, as well as demonstrated testosterone levels below a certain threshold. The requirement of having undergone surgery to remove male genitalia is expected to eliminate many potential athletes from competing against athletes of the opposite sex because the procedure remains relatively rare within the transgender community.

The new rules are sure to stir up the already heated debate about men competing against women in both amateur and professional athletics in America. Ohio’s Republican governor, Mike DeWine, has been under fire from conservatives since he vetoed a bill last week that would have restricted the ability of transgender athletes to cross classes.

Among the most vocal critics of the trend is female swimmer Riley Gaines, who has led campaigns across the country to exclude transgender men from female sports after being defeated in a national contest against a transgender swimmer, Lia Thomas. In a social media post, Ms. Gaines described USA Boxing’s decision as a “slippery slope.”

“Allowing men to punch women in the name of ‘compassion & inclusivity’ is incomprehensibly despicable,” Ms. Gaines said. “Men will be glorified for beating up on women. Not only glorified, they will be deemed ‘brave’ for such actions.”

Another notable female athlete, tennis champion Martina Navratilova, who has drawn harsh criticism from the LGBT community for her opposition to men competing against women, described the rule change as “beyond irresponsible” in a post on X, the platform formerly known as Twitter.

Another boxing body, the international World Boxing Council, which governs many professional matches, has proposed that transgender athletes compete in their own category entirely. The proposal, which has yet to be enacted, was panned by some athletes as “dehumanizing” to transgender athletes who would be permanently segregated in the sport.