NEW YORK — Nassau County Executive Bruce Blakeman has filed a lawsuit against New York Attorney General Letitia James after she threatened legal action over the county's recent anti-transgender sports ban.

The lawsuit was filed on Wednesday by Blakeman, a Republican, who 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."

"On behalf of the hundreds of thousands of women and girls in Nassau County, I have filed a federal lawsuit against @NewYorkStateAG to protect women’s sports and ensure a safe environment for women," Blakeman said in a post on X.

In a statement to ABC News, a spokesperson for the attorney general's office called the executive order "transphobic and discriminatory."

"Our laws protect New Yorkers from discrimination, and the Office of the Attorney General is committed to upholding those laws and protecting our communities," the statement said. "This is not up for debate: the executive order is illegal, and it will not stand in New York.”

Last week, James' office issued a cease-and-desist letter against his Feb. 22 executive order that bans transgender women and girls 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 Long Island County must expressly designate teams based on an athlete's sex assigned at birth for all sporting competitions or events.

Under the executive order, 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. These restrictions were set to go into effect immediately, according to Blakeman's office.

Blakeman's lawsuit argues that the executive order is not a ban on transgender athletes competing in sports: "The Executive Order invites transgender biological males to compete except in teams and leagues that advertise or identify as exclusively all-girls or all-women."

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

The attorney general's office argues that the order is "in clear violation of New York State anti-discrimination laws and demands that it be immediately rescinded."

"The Order’s immediate effect is to force sports leagues to make an impossible choice: discriminate against transgender women and girls, in violation of New York law, or find somewhere else to play," said the letter. "In addition to violating basic civil and human rights, the executive order will impose undue increased scrutiny on women’s and girls’ teams and leagues and will also subject all athletes on women’s and girls’ sports teams to intrusive and invasive questioning and other verification requirements."

Blakeman's lawsuit claims James' order violates the Equal Protection Clause of the Fourteenth Amendment and asks the court to enjoin James' office from taking action against the county and Blakeman for implementing the executive order.

In his response to the cease-and-desist letter, he said his executive order "stops the bullying of women and girls by transgender males who have many outlets to compete without putting the safety and security of females in danger."

The executive order 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 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.

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.

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.

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

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.

Local civil rights advocacy groups, including the New York Civil Liberties Union, argue that 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."

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