Shantel Jackson, referred to by the boxer as Miss Jackson when he dated her, also alleged false imprisonment and civil harassment in the lawsuit filed in Los Angeles County Superior Court and detailed by attorney Gloria Allred in a news conference.
A spokeswoman for Mayweather and the boxer's promoter did not immediately return phone calls and messages left them by the Los Angeles Times. Mayweather (46-0) is in training for a Sept. 13 title defense against Argentina's Marcos Maidana at MGM Grand in Las Vegas.
Jackson said she met Mayweather when she was a 21-year-old hostess in Atlanta in 2006 and later moved in with him in Las Vegas.
Allred cited two incidents that she contended were assault, adding that Jackson was at times forced to stay in Mayweather's home, allowed to depart only when accompanied by a Mayweather employee.
Allred said in her prepared statement Thursday that a December 2013 "sonogram revealed that Ms. Jackson was carrying twins that Mayweather had fathered, and she told him the news. He asked for a copy of the sonogram, which she sent to him. She had no idea that he would turn that image into a device to inflict emotional torture upon her.
"Mayweather insisted that the plaintiff move to Las Vegas. Ms. Jackson wanted to remain in Los Angeles. When Ms. Jackson refused to move, Ms. Jackson alleges that Mayweather became verbally abusive, stating 'I took you out of the 'hood. I should have left [you] there.'
"In January, Ms. Jackson's pregnancy terminated and Mr. Mayweather was so informed."
Just last week, Mayweather's father, Floyd Sr., said in an interview with The Times that something significant was bothering his son around the time of his hard-fought May 3 victory over Maidana.
Allred said Thursday in her statement that, "On May 1, Mayweather, in retaliation for Ms. Jackson's continued refusals to comply with his demands … decided to give her the ultimate humiliation. That day, knowing that his social media following was huge and devoted, Mayweather posted the following on his Facebook and Instagram accounts: "the real reason me and Shantel Christine Jackson @MissJackson broke up was because she got an abortion, and I'm totally against killing babies."
The post was distributed in Internet reports, Allred said.
Mayweather in 2012 served 60 days in a Nevada jail after the mother of his children, Josie Harris, claimed she was roughed up by the boxer when he learned she was seeing another man.
Jackson remained with Mayweather during his jail term.