Amanda Serrano accused Katie Taylor of backing out of a promise to fight 12 three-minute rounds as the rivals exchanged words at a surprisingly fiery news conference in New York.
Serrano even wore a headguard to the face-off, a nod to her accusation Taylor kept deliberately headbutting her in their last fight.
Taylor, 38, will defend her undisputed light-welterweight titles in the much-anticipated trilogy bout at the iconic Madison Square Garden in New York on 11 July.
The Irishwoman narrowly won both previous encounters, most recently a points decision in November in Texas.
Puerto Rico’s Serrano, 36, wanted the third fight to be over 12 three-minute rounds, rather than the 10 two-minute rounds used in women’s boxing.
“We shook on it. If you can roll the tapes, we shook on it. She didn’t agree when we went to sign the contract,” Serrano said.
“If that’s her choice then that’s her choice, but I believe that women should get the recognition and the equality that the men get.”
The pair have always insisted that while there is no friendship, they share a mutual respect.
But there was plenty of needle when a wide-eyed Serrano removed the headguard and stared into a smirking Taylor’s eyes, before they both departed the stage without a handshake or even a nod of acknowledgement.
