Idaho enacted House Bill 500 in March, with the bill referred to as the "Fairness in Women’s Sport Act."

The act states that "athletic teams or sports designated for females, women, or girls shall not be open to students of the male sex."

It adds that, if disputed, a student may establish their sex by presenting a signed physician's statement that shall indicate the student's sex based on "the student's reproductive anatomy, genetic makeup, or normal endogenously produced testosterone levels."

The bill states that there are "inherent differences between men and women", ranging from "chromosomal and hormonal differences to physiological differences."

Separate sex specific teams are viewed as means of "further efforts to promote sex equality", with teams accomplishing this by "providing opportunities for female athletes to demonstrate their skill, strength, and athletic abilities while also providing them with opportunities to obtain recognition and accolades, college scholarships, and the numerous other long-term benefits that flow from success in athletic endeavours."

The legislation has proved controversial with the NCAA facing calls to remove its events from the state.

The NCAA issued a statement saying the bill was harmful to transgender athletes and would be discussed at their board of governors meeting in August.

"As we have previously stated, Idaho’s House Bill 500 and resulting law is harmful to transgender student-athletes and conflicts with the NCAA’s core values of inclusivity, respect and the equitable treatment of all individuals," the NCAA said.

"Further, Board of Governors policy requires host sites to demonstrate how they will provide an environment that is safe, healthy, and free of discrimination, plus safeguards the dignity of everyone involved in the event.

"As such, the NCAA Board of Governors was scheduled to discuss the legislation and its implications to student-athletes at its August meeting.

"NCAA Championships are open to everyone, and the Association is committed to assuring that its events are safe and healthy for all who attend.

"It is our clear expectation that all NCAA student-athletes will be welcomed, treated with respect, and have non-discriminatory participation wherever they compete."

Former tennis star Billie Jean King, Women’s World Cup winner Megan Rapinoe and basketball star Sue Bird are among a list of 45 former or current athletes calling for the NCAA to move events out of Idaho.

Over 400 student athletes and a series of advocacy groups have also signed the letter, which was revealed by Sports Illustrated.

"We are writing to request you relocate all NCAA events, including the 2021 NCAA Men’s Basketball Championship games, from Idaho due to the state’s recent passage of dangerous anti-transgender legislation that prohibits certain groups of student athletes from participating in school sports.

"Given Idaho’s adoption of a discriminatory law that directly impacts college athletics, violates NCAA values, and undermines the dignity and well-being of NCAA athletes, Idaho schools no longer qualify to host NCAA events."

The letter says the law "forces women and girls to be subject to invasive medical procedures simply because they are, or are suspected to be, transgender" and labels the ban to be "extreme, harmful, and discriminatory."

The signatures argue the law "blatantly targets an already-marginalised community in athletics and decreases their participation in sports", adding that many transgender students already participate at significantly lower rates and feel unsafe in athletic spaces.

The NCAA previously moved seven of its events out of North Carolina in 2016 and 2017 over its "Bathroom Bill", which banned people from using public bathrooms that did not correspond to their biological sex as listed on their birth certificates.

North Carolina later modified the bill with NCAA events returning to the state.

The American Civil Liberties Union and Legal Voice filed lawsuits against the Idaho Bill in April.

The lawsuit was filed on behalf of Lindsay Hecox, a transgender athlete aiming to compete in athletics, as well as a fellow Boise High School student who is concerned about being subjected to invasive "sex verification" testing under the new law.

Two female students at Idaho State University have called for the lawsuit to be dismissed, with the Attorneys with Alliance Defending Freedom representing their case.

Madison Kenyon and Mary Marshall, who are on athletics scholarships at the university, say they have lost to a transgender athlete from the University of Montana and believe transgender athletes are unfair competition.

Kenyon, writing in an opinion piece for the Idaho Statesmen, argues that scientifically "the difference between male and female aren’t a matter of person opinion."

She expressed concerns NCAA events could soon become "men’s sports and co-ed sports" without a dedicated category for women.

Kenyon argues the law is necessary to ensure women’s opportunities are not sacrificed.

"Allowing males to enter women’s sports eliminates the connection between an athlete’s effort and her success," Kenyon wrote.

"That’s a key reason athletes love to compete.

"Sex separation in sports helps ensure that males and females both enjoy opportunities for fair competition and victory.

"It helps guarantee that, when women like me work hard, we have a shot at winning.

"It protects opportunities for success in women’s sports."