OKLAHOMA CITY (AP) — Oklahoma Gov. Kevin Stitt signed a bill Tuesday explicitly prohibiting the use of nonbinary gender markers on state birth certificates, a ban experts say is the first of its kind in the nation.

The bill followed a flap last year over the Oklahoma State Department of Health’s agreement in a civil case allowing a nonbinary option. The birth certificate in that case was issued to an Oklahoma-born Oregon resident who sued after the agency initially refused the request. People who are nonbinary do not identify with traditional male or female gender assignments.

News of the settlement prompted outrage among Republicans, including Stitt, who along with fellow conservatives in a number of GOP-led states have been engaged in a culture war over issues like restricting LGBTQ and abortion rights that drive the party’s base in an election year. Stitt’s appointee to lead the agency abruptly resigned the next day, and the governor then promptly issued an executive order prohibiting any changes to a person’s gender on birth certificates, despite the settlement agreement. A civil rights group has challenged the executive order in federal court, but the state has not yet responded.

Many states only offer male or female gender options on birth certificates, but Oklahoma is the first to write the nonbinary prohibition into law, according to Lambda Legal, the civil rights group suing Oklahoma.

Currently, 15 states and the District of Columbia specifically allow a gender marker designation outside of male or female, according to the National Center for Transgender Equality. That number will increase on July 1 when Vermont’s new statute goes into effect.

“People are free to believe whatever they want about their identity, but science has determined people are either biologically male or female at birth,” said Oklahoma Rep. Sheila Dills, the House sponsor of the bill, in a statement after the bill passed the House last week. “We want clarity and truth on official state documents. Information should be based on established medical fact and not an ever-changing social dialogue.”

Oklahomans in 2020 elected the nation’s first openly nonbinary legislator in the country, Oklahoma City Democrat Rep. Mauree Turner, who said it was painful to have colleagues single out those who are gender diverse.

“I find it a very extreme and grotesque use of power in this body to write this law and try to pass it — when literally none of them live like us,” Turner tweeted the day the bill was debated.

Republicans in conservative states across the country have introduced several bills this year targeting transgender and nonbinary people. Oklahoma’s governor earlier this year signed a bill prohibiting transgender girls from playing on female sports teams, one of many such bans being signed into law across the country. Other conservative states, including Alabama, Arkansas, Tennessee and Texas, have passed laws prohibiting gender-confirming treatments for minors.

The U.S. State Department recently announced it had issued its first passport with an “X” gender designation, marking a milestone in the recognition of the rights of people who do not identify as male or female, and expects to be able to offer the option more broadly next year.

Doctors and scientists say sex and gender are not the same thing. While sex typically refers to anatomy, gender identity is more an inner sense of being male, female or somewhere in between, regardless of physical anatomy, according to Dr. Jason Rafferty, a pediatrician and child psychiatrist at Hasbro Children’s Hospital in Rhode Island and a lead author of the American Academy of Pediatrics’ transgender policy.

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