Nassau County announces ban on trans women from competing in women's sports in county-run facilities

Republican Nassau County Executive Bruce Blakeman announced Thursday that he will use an executive order to ban transgender athletes from competing in events aligning with their gender identity in county-run facilities.

The executive order states that sports leagues, organizations, teams and other entities in the Long Island County must expressly designate teams based on an athlete's sex assigned at birth, when applying for a "use and occupancy" permit at a Nassau County Parks property for a sporting competition or event on all levels.

Permits will not be given to any event or competition that allows transgender women or girls to compete in girls' or women's sporting events. The order allows transgender men and boys to play in competitions for men and boys.

This will go into effect immediately, according to Blakeman's office.

The move goes against guidelines from local and national sports associations.

The New York State Public High School Athletic Association's transgender policy states that it is "committed to providing all students with the opportunity to participate ... in a manner consistent with their gender identity and the New York State Commissioner of Education's Regulations."

The National Collegiate Athletic Association transgender guidelines vary from sport to sport. Transgender student-athletes typically need to document sport-specific testosterone levels at the beginning of their season and a second documentation six months later, and then another documentation four weeks before championship selections.

The governing bodies of several national and international sports leagues, including the International Olympic Committee, require transgender women to meet certain hormone levels in order to play on sports teams with cisgender women.

There is no clear data on whether transgender women have an advantage physiologically, according to health experts.

One study in the British Journal of Sports Medicine found that the athletic advantages of the 46 trans women over their cisgender counterparts declined with feminizing therapy. However, this study also found theyhad a 9% faster mean run speed than cisgender women after a one-year period of testosterone suppression. A different study in the American Journal of Sports Medicine found that there is not yet any direct or consistent research suggesting transgender women have an athletic advantage at any stage of their transition.

Experts wrote in a recent JAMA Pediatrics editorial that preventing trans youth from participating in school sports could be bad for the mental and physical health of an already at-risk population because they lose out on the developmental benefits of sports participation.

Restrictions on hormone levels have impacted athletes with differences in sex development, including track star Caster Semenya, who was born intersex and has naturally high testosterone levels.

Blakeman, a Republican, said he believes the designation of separate athletic teams or sports based on sex assigned at birth "is necessary to maintain fairness for women's athletic opportunities."

"Women and Girls hard work, on-field achievements, and athletic futures deserve to be fostered, nurtured, and celebrated," Blakeman stated in the executive order.

Local civil rights advocacy groups, including the New York Civil Liberties Union, argued the executive order is illegal.

"Requiring girls who are trans to compete on boys' teams effectively bars them from sports altogether," NYCLU said in a statement to ABC News. "Participating would mean being outed and being denied the same opportunities other girls enjoy: to challenge themselves, improve fitness, and be part of a team of their peers."