The organization that governs international swimming has, for all intents and purposes, banned transgender women from competing in top-level international women’s competitions. The decision intensifies the debate on sports and gender issues that is raging in US state legislatures and is causing increasingly serious divisions between parents, athletes and coaches in all categories of sport.

A vote by FINA (International Swimming Federation), which administers international water sports competitions, has banned transgender women from competing unless they undergo medical treatments that suppress testosterone production before one of the first stages of puberty or before the age of 12, whichever is later.

The ruling establishes one of the strictest rules barring transgender athletes from competing in international sports. Scientists believe that the onset of male puberty gives transgender women a lasting physical advantage over female-born athletes.

International swimming has also proposed establishing a new “open” category for athletes who identify as female but do not qualify to compete against born females.

More than 70% of the federations that make up FINA voted in favor of adopting the rule, drawn up in November by a working group that included athletes, scientists and legal and medical experts. The rule came into effect this Monday (20), days before the start of the World Swimming Championships in Budapest, Hungary.

“We have to protect our athletes’ right to compete, but we also have to protect the fairness of competition in our tournaments, especially in the women’s categories of FINA competitions,” said the organization’s president, Husain al- Musallam, in a statement.

There are no competitions for transgender women at the world swimming championships, and only one transgender woman, a Canadian soccer player, has won an Olympic medal so far as far as is known.

The decision, however, came just three months after Lia Thomas became the first transgender woman to win a Division 1 swimming championship in the NCAA, the organization that governs college athletics in the United States (she won the 500 meter freestyle), and that put the issue in the spotlight. Thomas said she hoped to qualify for the United States Olympic team in 2024. Under the new rules, she would not be eligible to compete.

Fina’s rules only apply to international competitions, but could guide the thinking of other sports federations tackling the issue.

Activists said the decision by the international swimming organization represents a step forward for the growing movement to stop transgender women from participating in recreational sports. They said the limitation undermines efforts to provide everyone with full access to the sport, regardless of the gender they were assigned at birth.

Translation by Paulo Migliacci