Judge Charles Atchley Jr from the Eastern District of Tennessee, who was appointed by former US President Donald Trump, ruled that Title IX guidance from the Joe Biden administration would have made it impossible for some states to enforce their own laws on transgender athletes competing in girls' and women's sport.

It means that states with laws limiting the participation of transgender athletes can enforce them.

The ruling also applies to trans individuals' access to bathrooms and changing facilities.

The ruling came after a coalition of 20 Republican attorneys general - led by Tennessee's Herbert Slatery - filed a lawsuit against the Federal Government last year, claiming they faced losing funding due to national directives conflicting with their own state laws.

Atchley wrote that states "cannot continue regulating pursuant to their state laws while simultaneously complying with defendants' guidance" in explaining the reasons for the decision, as reported by Reuters.

The appealing attorneys general argued that the directives improperly expanded on the Bostock v Clayton County ruling the US Supreme Court made in 2020, which increased anti-discrimination protections for transgender workers.

The Justice Department, the Department of Education and the Equal Employment Opportunity Commission, who were the defendants in the lawsuit, asked Atchley to dismiss the case but this was denied.

The judge's ruling means competitors like student-athlete Lia Thomas, a transgender swimmer who competes in women's races, could face increased barriers to entry.

Thomas won the 500 yards freestyle race at the NCAA Swimming Championships in March, making history as the first openly transgender athlete to win an NCAA Division I title.

This vaulted Thomas into the centre of the debate of transgender participation in women's sport.

Thomas, who previously competed for the men's team before undergoing a medical transition, is one of the University of Pennsylvania's nominees for the NCAA's 2022 Woman of the Year Award.

NCCA regulations required Thomas to go through months-long medical treatment before being allowed to compete against women, leading to Thomas undergoing 30 months of testosterone-reducing hormone therapy.

Thomas has said the transition was not to gain a competitive advantage, but to be "happy" and "true" to herself.

Thomas has also expressed a desire to compete at the Paris 2024 Olympics, but a landmark International Swimming Federation (FINA) ruling which requires trans women to have transitioned by the age of 12 or prove they have "not experienced any part of male puberty beyond Tanner Stage 2" - when physical development kicks in - to be able to compete in women's competition has made Thomas ineligible.

Given the difficulties associated with transition and the small likelihood of swimmers being able to complete it at such a young age, the policy has been viewed as an effective ban on trans women's participation.

The Federation of Gay Games criticised the policy as "discriminatory and exclusive", although FINA President Husain Al-Musallam said he wants to create an "open category" where trans women would be able to compete.

FINA's ruling has increased scrutiny on sport's policies over transgender participation, with the International Olympic Committee handing responsibility to individual International Federations (IFs) to form their own rules.

Several IFs have confirmed since the FINA ruling that they are reviewing their own policies, including International Rugby League choosing to prevent transgender athletes from playing in women's international matches until it has been able to conduct further research.

Transgender rights, including the permission for trans women and girls to compete in women's sport, is an issue of major cultural divide in the US.

President Biden vowed to champion equality and trans rights during his election campaign.

Since becoming President, Biden has reversed a ban on transgender servicemembers, sought to stop transgender children being preventing access to gender-affirming healthcare and issued the guidance for trans athletes to be allowed to compete in women's sport, which has now been overruled this ruling.