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Sen. Marco Rubio, R-Fla., urged USA Boxing in a letter obtained by Fox News Digital on Friday to reverse its decision to allow transgender female athletes to compete against women in the ring.

USA Boxing says a fighter who transitioned from male to female can compete in the female category under several conditions spelled out in the rule book: "The boxer identifies as a female and has completed gender reassignment surgery. The fighter has undergone quarterly hormone testing and gives the organization documentation of hormone levels for a minimum of four years. The fighter’s testosterone levels have been below 5 nanomoles per liter 48 months before their first fight, the fighter’s total testosterone level must remain below 5 nmol/L through their eligibility to compete against females and the conditions will be monitored and tested at the fighter’s expense with a 12-month suspension for failing to meet the standards."

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Marco Rubio in October

Sen. Marco Rubio, R-Fla., is urging USA Boxing to reverse its decision to allow transgender female athletes to compete against women in the ring. (Bill Clark/CQ-Roll Call Inc. via Getty Images)

Rubio urged USA Boxing Executive Director and CEO Mike McAtee to reverse the decision, saying the policy "denies the scientific reality of sex, endangers women, upends fairness in athletics, and diminishes womanhood by pretending it is only a matter of surgery and hormone levels."

"Moreover, your policy encourages athletes suffering from gender dysphoria to castrate themselves in order to compete. I write to urge you to reverse this dangerous decision," the letter reads.

Rubio pointed to the results of transgender fighter Fallon Fox’s matches. Rubio said Fox’s bouts resulted in three knockouts in the ring, including serious injuries to the female opponents. He also pointed to World Boxing Council President Mauricio Sulaiman, who said men shouldn’t be fighting women.

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Rubio questions Blinken

Sen. Marco Rubio, R-Fla., pointed to the results of transgender fighter Fallon Fox’s bouts, which Rubio said resulted in three knockouts in the ring, including serious injuries to the female opponents. (Bill Clark/CQ-Roll Call Inc. via Getty Images)

"Allowing men to hit women is reprehensible, even under the guise of athletic competition. It is behavior no civilized country would tolerate, much less encourage," Rubio wrote. "Civilized countries enforce special prohibitions on violence against women because there are differences between men and women that make men more capable of violence. Men have more muscle mass, larger hearts and lung capacity, and denser and larger skeletal structures, among other advantages.

"These advantages allow men to overpower and endanger women past the point of fair competition. Hormone injections and monitoring cannot remove these innate, biological advantages. Even if they could, that would not change the fundamental principle that it is wrong for men to hit women."

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Rubio added that pressure from pro-transgender activists is "no excuse to disregard and endanger athletes in the process."

USA Boxing didn’t immediately respond to a request for comment from Fox News Digital.

The organization’s decision was announced late last month.

Boxing stars Ebanie Bridges, Claressa Shields and Amanda Serrano.

Boxing champions Ebanie Bridges, left, and Amanda Serrano, right, spoke out about the issue, as did Olympic medalist Claressa Shields, center. (Getty Images)

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Boxing champions Ebanie Bridges and Amanda Serrano spoke out about the issue, as did Olympic medalist Claressa Shields.

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