The Court of Arbitration for Sport (CAS) confirms the registration of the request for arbitration submitted by US transgender swimmer Lia Thomas (the Athlete), which seeks to challenge certain parts of World Aquatics' Men's and Women's Competition Category Eligibility Policies and Related Operational Requirements effective as of 24 March 2023 (the disputed provisions). 

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

However, she contends that the challenged rules are invalid and unlawful because they discriminate against her in violation of the Olympic Charter, the World Aquatics Constitution, and Swiss law including the European Convention on Human Rights and the Convention on the Elimination of All Forms of Discrimination against Women; and that such discrimination cannot be justified as necessary, reasonable, or proportionate to achieve a legitimate sporting objective.

By bringing the matter before CAS, Ms Thomas seeks an order from the CAS declaring the challenged provisions to be unlawful, void and of no force or effect. 

The CAS Arbitration was commenced in September 2023. Following the Code of Sports-related Arbitration, this "ordinary" arbitration procedure (i.e., not an appeal) was subject to strict confidentiality rules applicable to CAS proceedings. The parties involved in this case have now agreed that general information about the proceedings themselves will be provided by the CAS Registry. A hearing date has not yet been set. 

The registration of this case coincided with the reference number 10’000, which is the number of arbitrations (and previous hearings, but excluding ad hoc proceedings and mediations) registered by the CAS since its creation in 1984. As of 31 December 2023, the CAS had registered a total of 10,638 cases (all cases included) since its creation and 943 in 2023 alone. 

Swimmer Lia Thomas became the first transgender woman to win the top US collegiate national title in 2022, and is asking CAS to allow her to return to elite women's competition. 

In June 2022, World Aquatics voted to ban transgender women who have undergone male puberty from competing in women's races. Previously, transgender women could compete as long as they lowered their testosterone levels. However, a scientific panel found that even after lowering their testosterone levels with medication, transgender women still had a significant advantage.