Riley Gaines calls on famous female athletes to choose a side in trans debate. Here's who she's starting with

Former NCAA swimmer Riley Gaines says the future of women's sports relies on girls refusing to compete against transgender athletes, sacrificing their title.

Riley Gaines, a former NCAA swimmer who speaks out against trans athletes competing in girls and women’s sports is calling on famous female athletes to join her cause.

"Each day for the next week I'm going to call on well-known female athletes to take a stance on this issue because silence is complicity...we need their voices," Gaines, who swam with the University of Kentucky, tweeted.

Her first tweet asked the world-famous tennis star sisters Serena and Venus Williams how they "feel about males competing against women."

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Gaines became outspoken on preserving women’s sports for biological females after tying for fifth with transgender swimmer Lia Thomas in the 200-meter NCAA championship last year.

In 2013, Serena Williams, considered one of the best female tennis players of all time, told David Letterman that she preferred to play against women.

"The men are a lot faster, they serve harder, they hit harder," Serena said. "It's a completely different game."

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"If I were to play Andy Murray, I would lose, 6-0, 6-0, in 5 to 6 minutes, maybe 10 minutes," Serena said the top British tennis star.

Former NCAA swimmer Riley Gaines called on tennis star Serena Williams how she feels "about males competing against women." (AP Photo/Seth Wenig)

"I'm with you," Letterman said jokingly. "When it comes to tennis, I only want to play girls."

Gaines recently told Fox News that allowing biological men into women’s sports "doesn’t work."

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