- Women's bouts are usually contested over 10 two-minute rounds.
- "I am the only boxer, male or female, from Puerto Rico, to become an undisputed champion."
Featherweight world champion Amanda Serrano has vacated her WBC title after the organisation refused to sanction 12 three-minute round contests.
Serrano, 35, retained her WBA, WBO and IBF titles against Danila Ramos by unanimous decision in October.
Women's bouts are usually contested over 10 two-minute rounds.
"The WBC has refused to evolve the sport for equality, so I am relinquishing their title," Puerto Rico's Serrano posted on Instagram.
"Thank you to the sanctioning bodies who have evolved for equality. If you want to face me in the ring, you have a choice. I've made mine."
Serrano's WBC title was not on the line as the Mexico City-based sanctioning body would not endorse extending the length of the rounds in female boxing, citing "health and safety" concerns.
It was the first time since 2007 that women have been in the ring for a title fight for as long as their male counterparts.
"I am the only boxer, male or female, from Puerto Rico, to become an undisputed champion. I am the only female boxer to have won titles in seven divisions," Serrano said.
"I am the first female boxer, along with Katie [Taylor] to headline Madison Square Garden. I am the first female boxer to make seven figures from a fight and the same from sponsors.
"And I am the first undisputed female champion to fight 12x3 minute rounds.
"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."
Earlier this year, more than 20 current and former women boxers, including Serrano, signed a statement saying they wanted to be able to fight three-minute rounds.
Advocates for three-minute rounds argue more time spent in the ring increases the chance of a knockout and consequently a better spectacle.
Serrano and Ramos went the full 36-minute distance, with Serrano winning all 12 rounds.