Featherweight champion Amanda Serrano on Wednesday vacated her WBC title after they refused to allow her to take part in bouts under the same rule-set as men's boxing, which includes 12 three-minute rounds.
The rounds in women's championship fights are two minutes each and are typically scheduled for no more than 10 rounds.
Serrano, who had unified the WBA, WBC, IBF, WBO, IBO and Ring Magazine titles, was among the women boxers who started a campaign in October to have the option to compete under the same rules as men.
The Puerto Rican fought Danila Ramos to a unanimous decision victory later that month, which was the first time a women's title fight was fought in 12 three-minute rounds.
WBC did not sanction the fight, while the other sanctioning bodies recognised the bout as a title defence for the 35-year-old.
"The WBC has refused to evolve the sport for equality. So I am relinquishing their title," Serrano wrote on Instagram.
"Moving forward if a sanctioning body doesn’t want to give me and my fellow fighters the choice to fight the same as the men, then I will not be fighting for that sanctioning body."
WBC President Mauricio Sulaiman had earlier said that they won’t allow 12 three-minute rounds in women's bouts.
"Tennis, women play three sets. Basketball, the basket is shorter and the ball smaller and those are not contact sports. We stand by safety and well-being of the fighters," Sulaiman wrote on X, formerly Twitter, in September.
Both Serrano and Ramos were able to fight under the new rules without damage or incident, Serrano posted on X.
"It’s something I’ve wanted for years and finally now that I’m in the position, I will continue my career under that rule," she added.