The Rugby Football Union faces legal action against its ban on transgender women playing female contact rugby in England.
Transgender player Julie Curtiss has mounted a legal challenge against the decision, the Daily Telegraph reported.
The RFU says it will “robustly defend” the case.
The Telegraph said that Curtiss has issued the RFU with a pre-action protocol letter, a legal document written to resolve a dispute before court proceedings start.
She says the policy discriminates against her under section seven of the Equality Act 2010.
The legislation legally protects people from discrimination in the workplace and wider society, but there are exceptions when it comes to sport.
Section 195 says it is lawful to restrict the participation of transgender people from sporting competitions where physical strength, stamina or physique are important factors in deciding who wins.
However, the restriction can only be done to ensure the competition is fair or the other competitors are safe.
Essentially that means it would not be unlawful discrimination to refuse participation to a transgender athlete if the competition organisers can show they would have an unfair competitive advantage.
Curtiss, 52, hoped to play for Hove RFC’s women’s team for the 2023-23 season.
A six-page letter, submitted to the RFU via the London-based law firm Russell Cooke, said: “It is difficult to see how a blanket ban with no exceptions could be justified as necessary.
“Allowing a particular trans woman to play in the female category for contact rugby may not raise any issues in respect of fair competition or the safety of competitors, and if so her exclusion cannot be justified.”
The RFU has until 30 September to respond.
“We are in receipt of a pre-action letter of claim and will be responding via our appointed lawyers,” an RFU spokesperson said.
“We believe any potential claim is without merit and we will robustly defend the case.”
The Rugby Football League announced a similar ban in July, while other sports have been assessing their approach.
Fina, swimming’s world governing body, voted to stop transgender athletes from competing in women’s elite races if they have gone through any part of the process of male puberty.
It is aiming to establish an ‘open’ category at competitions, for swimmers whose gender identity is different than their birth sex.
Cycling’s governing body, the UCI, toughened its rules on transgender eligibility by doubling the period of time before a rider transitioning from male to female can compete.