American swimmer Lia Thomas, who became the first transgender athlete to win the highest US national college title when she triumphed in 2022, is taking legal action in a bid to compete again in elite female sport.

Two years ago governing body World Aquatics voted to stop transgender women from competing in women’s elite races if they have gone through any part of the process of male puberty.

Up until then transgender women could compete as long as they lowered their testosterone levels.

But Thomas, 25, is taking a case to the Court of Arbitration for Sport (CAS) in Switzerland to try to fight the ban.

“Ms Thomas accepts that fair competition is a legitimate sporting objective and that some regulation of transgender women in swimming is appropriate,” Cas said.

“However, Ms Thomas submits that the Challenged Provisions are invalid and unlawful as they discriminate against her.”

The body said arbitration started in September and “was subject to strict confidentiality rules” but involved parties had “now agreed that general information concerning the procedure itself be communicated”.

No hearing date has yet been set, Cas added.

In a statement issued to BBC Sport, Brent Nowicki, the executive director of World Aquatics, said: “[Our] policy on gender inclusion, adopted by World Aquatics in June of 2022, was rigorously developed on the basis of advice from leading medical and legal experts, and in careful consultation with athletes.

“World Aquatics remains confident that its gender inclusion policy represents a fair approach, and remains absolutely determined to protect women’s sport.”

Thomas is yet to comment. In 2022 she said she hoped to compete in the US trials for the Paris 2024 Olympics and that transgender athletes were “not a threat” to female competitors.

A host of governing bodies – including in cycling and athletics – have also banned transgender athletes from elite female competition over the past two years, with officials stating they are prioritising fairness and safety over inclusion.

Thomas won the US national college title with victory in the women’s 500-yard freestyle last year.

Thomas swam for the Pennsylvania men’s team for three seasons before starting hormone replacement therapy in spring 2019.

Speaking at the time World Athletics president Lord Coe said: “I think that the integrity of women’s sport if we don’t get this right, and actually the future of women’s sport, is very fragile.”