Female transgender athletes who transitioned after male puberty will no longer be able to compete in women’s races, world cycling governing body the UCI said Friday.

The decision came after American rider Austin Killips became the first openly transgender woman to win an official cycling event earlier this year.

“From now on, female transgender athletes who have transitioned after (male) puberty will be prohibited from participating in women’s events on the UCI International Calendar — in all categories — in the various disciplines,” the international federation said in a statement.

The UCI said the ban, starting on Monday, was necessary to “ensure equal opportunities.”

Killips rode to victory in the fifth stage of the Tour of the Gila, one of the marquee U.S. stage races. Her victory provoked a negative reaction by some cycling fans and former racers despite the 27-year-old athlete having adhered to a policy put in place by the UCI last year requiring transgender athletes to have serum testosterone levels of 2.5 nanomoles per liter or less for at least 24 months before competing in women’s events.

The UCI said Friday it “has taken note of the state of scientific knowledge, which does not confirm that at least two years of gender-affirming hormone therapy with a target plasma testosterone concentration of 2.5 nmol/L is sufficient to completely eliminate the benefits of testosterone during puberty in men.”

It also noted the difficulty to “draw precise conclusions about the effects” of gender-confirming hormone therapy.

“Given the current state of scientific knowledge, it is also impossible to rule out the possibility that biomechanical factors such as the shape and arrangement of the bones in their limbs may constitute a lasting advantage for female transgender athletes,” the UCI added.

Despite the ban, UCI president David Lappartient said “the UCI would like to reaffirm that cycling — as a competitive sport, leisure activity or means of transport — is open to everyone, including transgender people, whom we encourage like everyone else to take part in our sport.

It also noted the difficulty to “draw precise conclusions about the effects” of gender-confirming hormone therapy.

“Given the current state of scientific knowledge, it is also impossible to rule out the possibility that biomechanical factors such as the shape and arrangement of the bones in their limbs may constitute a lasting advantage for female transgender athletes,” the UCI added.

Despite the ban, UCI president David Lappartient said “the UCI would like to reaffirm that cycling — as a competitive sport, leisure activity or means of transport — is open to everyone, including transgender people, whom we encourage like everyone else to take part in our sport.