Sporting greats Billie Jean King, Greg Louganis and Martina Navratilova are backing a campaign to stop Egypt and Russia removing an anti-homophobia commitment in the Olympic Truce Resolution.
Agreed at the United Nations every two years, the resolution is meant to promote Olympic values during the Games and one week before and after.
In 2015, for the first time, it included a reference to the Olympic Charter's Principle 6, which prohibits discrimination on the basis of sexual orientation.
This year's vote is set for Monday but Egypt and Russia have already made their opposition to its inclusion clear.
In response, two US-based campaign groups for LGBTQ rights - OutRight Action International and Athlete Ally - have joined forces to resist their efforts to lobby against Principle 6.
"Sport and society thrive when we embrace the diversity of our world," Rio 2016 women's basketball champion Breanna Stewart said in a joint statement on Wednesday.
"The Olympic spirit is grounded in inclusion, fair play and solidarity and the explicit mention of Principle 6 within the Olympic Truce Resolution sends a clear message that we take these values seriously."
The American star is one of 17 athletes, including former tennis greats King and Navratilova and Olympic diver Louganis, who have signed an open letter to the UN's general assembly.
"We're witnessing the greatest expansion of athletic activism in modern history - never before have we seen athletes speaking out so regularly for the protection and inclusion of the LGBTQ community," Athlete Ally founder Hudson Taylor added.
