Republican governor Kay Ivey signed legislation restricting transgender students from participating in K-12 sports, making Alabama the latest conservative state to ban transgender girls from playing on female sports teams.

Ms Ivey’s office announced in an email that she had signed the bill that says a public K-12 school “may never allow a biological male to participate on a female team”.

Asked if the governor had a comment on the decision, spokeswoman Gina Maiola said she could confirm the governor signed the bill on Friday but did not elaborate.

Supporters of the bill, HB 391, say transgender girls are born bigger and faster and have an unfair advantage in competition.

Opponents argue the bills are rooted in discrimination and fear, and violate the federal law barring sex discrimination in education.

“HB 391 is nothing more than a politically motivated bill designed to discriminate against an already vulnerable population.

“By signing this legislation, Governor Ivey is forcefully excluding transgender children.

“Let’s be clear here: transgender children are children.

“They deserve the same opportunity to learn valuable skills of teamwork, sportsmanship, and healthy competition with their peers,” Human Rights Campaign President Alphonso David said in a statement.

The Alabama House voted 74-19 for the bill sponsored by Republican Representative Scott Stadthagen of Hartselle.

The Alabama Senate voted 25-5 for the legislation.

“I want to thank Governor Ivey for her leadership and for protecting the rights of Alabama’s female athletes.

“Standing up for what is right is not always easy, but it is always the right thing to do,” Mr Stadthagen said on Friday.

During Senate debate on the bill last week, Republican Senator Garlan Gudger of Cullman said it is “unfair for biological males to compete and beat females in high school sports”.

He said the bill is needed to protect the integrity of female athletic programmes.

Across the country, Republican legislators have been hard-pressed to come up with actual instances in which a transgender girl’s participation has caused a problem on a girls sports team.

Mississippi Republican governor Tate Reeves last month signed a bill to ban transgender athletes from competing on girls or women’s sports teams.

Idaho last year became the first state to pass such a ban, but it faces a legal challenge.

Kansas governor Laura Kelly vetoed a bill banning transgender students from girls and women’s school sports.

She said the Republican-backed measure is a jobs killer that harms children.

Critics of such bills are worried that the measures could cost states from hosting sporting events.

Senate Minority Leader Bobby Singleton said last week that the bill will give Alabama a “black eye” as the state tries to recruit industries and sporting events to the state.

“We are spending too much time on craziness like this,” Mr Singleton said.

As similar bills crop up across the county, the NCAA, which regulates college athletics in the US expressed support for transgender athletes and warned that championships will only be held in locations “free of discrimination”.

“We will continue to closely monitor these situations to determine whether NCAA championships can be conducted in ways that are welcoming and respectful of all participants,” the NCAA statement read.

The NCAA currently requires transgender women to get drug treatment to lower their testosterone levels before they can compete in women’s sports.