Former NCAA swimming champion Lia Thomas is officially challenging World Aquatics policies that restrict transgender swimmers’ Olympic eligibility, the athlete’s lawyers confirmed this week.

As first reported by conservative U.K. newspaper The Telegraph and confirmed by NBC News on Friday, Thomas filed a dispute with the international Court of Arbitration for Sport (CAS) in Switzerland last September. The dispute challenges several recently introduced World Aquatics policies that disqualify most trans women and intersex people from international women’s swimming competitions like the Olympics and the Swimming World Cup, instead forcing them to compete in a new “open” category.

Carlos Sayao, a partner at the Canadian law firm Tyr, which is representing Thomas, called these policies “discriminatory” in brief comments to The Telegraph this week.

“Trans women are particularly vulnerable in society and they suffer from higher rates of violence, abuse and harassment than cis women,” Sayao told the paper, arguing World Aquatics’ policies would bring “profound harm to trans women.”

Though it was filed more than four months ago, the dispute between Thomas and World Aquatics was not immediately publicized because CAS arbitration is confidential by default. It’s unclear as to how the CAS judges will rule on Thomas’ complaint, but the body has defended other restrictions on trans and intersex athletes in the past. In 2019, the CAS ruled against intersex runner Caster Semenya in favor of World Athletics policies that restricted athletes’ hormone levels. Even though those policies were “discriminatory,” the court found, “such discrimination is a necessary, reasonable and proportionate means” of governing sports competitions.

But even though the CAS is considered the “Supreme Court of sport,” if Thomas should lose this dispute, she could still turn to the appeals process. After losing in the CAS, Semenya appealed her case to the Federal Supreme Court of Switzerland. Despite losing there as well, Semenya finally appealed again to the European Court of Human Rights, which ruled in her favor in 2023, awarding Semenya around $66,000 in damages from the Swiss government. Still, World Athletics and the Swiss government have contested that decision in turn, and are currently still enforcing those hormonal policies — even adopting new, broader restrictions.