World Rugby has announced transgender women cannot compete at the elite and international level of the women's game, becoming the first international sports federation to implement the rule.
Saturday's (NZ time) announcement comes after "a comprehensive, collaborative and inclusive review of its existing guidance" and their decision that transgender women can't play contact rugby at a high level was based"on safety grounds".
A report published by World Rugby earlier in the years said there was a "20-30 percent greater risk" of injury if a female player was tackled by someone who had gone through male puberty.
Transgender men remain permitted to play men's contact rugby.
World Rugby did say though that national unions can be flexible in their application of the guidelines at a community level.
"This has been a complex and emotive process, but a necessary one," says Dr Araba Chintoh, who chaired the review.
"We set out to determine whether it would be possible to maintain inclusion in contact rugby based on the available research and evidence and rugby's unique context of combining strength, power, speed and endurance in a physical, collision environment.
"As we progressed through a comprehensive and inclusive review, it became clear there are compelling evidenced safety considerations which we simply cannot ignore.
"Unions will be able to exercise flexibility on a case-by-case basis at the community level of the game, for which the unions are responsible, while World Rugby will continue to prioritise inclusion strategies to ensure that the trans community remain an active, welcome and important member of the rugby family."
Earlier this year, New Zealand Rugby chief operating officer Nicki Nicol said the governing body did not track gender identity in their player registrations but said they wanted to get better information.
World Rugby boss Sir Bill Beaumont said it was a hard decision to make.
"Rugby is a welcoming and inclusive sport and, while this has been a difficult decision to make, it has been taken following comprehensive consultation and engagement and for the right reasons, given the risk of injury,' he says.
"That said, we recognise that the science continues to evolve, and we are committed to regularly reviewing these guidelines, always seeking to be inclusive."
