Five-time Olympic basketball champion Sue Bird, football stars Megan Rapinoe and Becky Sauerbrunn and Paralympic wheelchair basketball gold-medallist Abby Dunkin are among the group of 40 athletes that put their names to the letter that has been sent to the US House of Representatives.

The opposition was organised by Athlete Ally, advocacy group for LGBTQ+ (lesbian, gay, bisexual, transgender, queer plus others) inclusion.

The letter sees athletes voice their criticism of the "Protection of Women and Girls in Sports Act", also known as "HR 734", which has recently been introduced to the US House of Representatives.

Republican politicians are behind the Bill that is seeking to amend the landmark Title IX of the 1972 Education Amendments Act so that "in athletics, sex shall be recognised based solely on a person’s reproductive biology and genetics at birth".

The 40 athletes claimed that the Bill was putting the human rights of trans athletes "under attack".

"If this Bill passes, transgender and intersex girls and women throughout the country will be forced to sit on the sidelines, away from their peers and their communities," the letter read.

"Furthermore, the policing of who can and cannot play school sports will very likely lead to the policing of the bodies of all girls, including cisgender girls.

"This will deter girls from participating in sports and create additional barriers.

"Denying children access to a place where they can gain significant mental and physical health benefits and learn lifelong lessons that come from being part of a team and working hard towards your goals does not protect women in sports.  

"We believe that gender equity in sport is critical, which is why we urge policymakers to turn their attention and effort to the causes women athletes have been fighting for decades, including equal pay, an end to abuse and mistreatment, uneven implementation of Title IX, and a lack of access and equity for girls of colour and girls with disabilities, to name only a few.

"Our deepest hope is that transgender and intersex kids will never have to feel the isolation, exclusion and othering that H.R. 734 is seeking to enshrine into law."

Joe Biden’s Democrat administration last week outlined a proposal to forbid schools from impose outright bans on transgender athletes.

Under the plans revealed by the US Department of Education, schools would be unable to bar trans students from playing sport but allows them to develop team eligibility rules.

"Every student should be able to have the full experience of attending school in America, including participating in athletics, free from discrimination," said US Secretary of Education Miguel Cardona.

"Being on a sports team is an important part of the school experience for students of all ages."

The proposal drew criticism from Democrat Alexandria Ocasio-Cortez, who described it as "indefensible and embarrassing" as she argued that it did not fully protect trans students.

White House press secretary Karine Jean-Pierre insisted that the Biden administration supported the LGBTQI+ community.

"We are so proud of the kids across this country who have organised protests and school walkouts to tell the politicians in their states to stop this legislative bullying," said Jean-Pierre.

"I know that these political attacks can really take a toll on people’s mental health.

"So I want to say directly to LGBTQI+ kids, you are loved just as you are, just the way you are."