The world’s swimming governing body, FINA, is bringing in new restrictions which effectively ban Transgender women from competing in women’s categories, over concerns about fairness in competition.

The decision was made in a vote amongst 152 national federations at the world championships in Budapest, with 71% in favour of the new policy which comes into effect today, June 20.

The new policy, which is 34 pages in length, states that Transgender athletes will be eligible to compete “provided they have not experienced any part of male puberty beyond Tanner Stage 2 [which marks the start of physical development], or before age 12, whichever is later”.

However, the spokesperson for FINA president Husain Al-Musallam told the Associated Press that “This is not saying that people are encouraged to transition by the age of 12 … They’re not saying everyone should transition by age 11, that’s ridiculous. You can’t transition by that age in most countries and hopefully wouldn’t be encouraged to. Basically, what they’re saying is that it is not feasible for people who have transitioned to compete without having an advantage.”

Under the new policy, there are plans to implement a new “open category” in which Transgender can compete in certain swimming competitions but Al-Musallam admits that “no one knows how it’s going to work”.

Megan Rapinoe, a US soccer veteran, has come out strongly opposed to the new policy, which she has called “cruel” and “disgusting”.

“Show me the evidence that trans women are taking everyone’s scholarships, are dominating in every sport, are winning every title. I’m sorry, it’s just not happening,” she said.

She also told TIME, “I’m 100 per cent supportive of trans inclusion. People do not know very much about it. We’re missing almost everything. At the highest level, there is regulation. In collegiate sports, there is regulation. And at the Olympic and professional level. It’s not like it’s a free-for-all where everyone’s just doing whatever.”

The development of this policy follows the victory of Transgender swimming athlete Lia Thomas who became the 500-yard freestyle champion at the US collegiate championships in Atlanta. Her success was criticised by many, despite data which showed that she had no biological advantage over her competitors, and the new restrictions mean her dreams of competing at the 2024 Olympics in Paris are unlikely to come to fruition.