The unbeaten Mayweather publicly challenged and taunted the Filipino superstar on Tuesday, daring Pacquiao to meet him May 5 in Las Vegas.
"Manny Pacquiao I'm calling you out let's fight May 5th and give the world what they want to see," Mayweather tweeted.
Moments later, Mayweather tweeted: "My Jail Sentence was pushed back because the date was locked in. Step up Punk."
Mayweather is available for a fight in May at the MGM Grand Garden after a judge agreed last week to postpone his jail sentence in a domestic violence case until June. Mayweather was sentenced to 87 days in jail, but likely will serve less time.
Mayweather and Pacquiao are boxing's top two stars, and they have circled each other warily for more than two years. Both have said they're eager to fight, yet still haven't reached a deal for what's likely to be the most lucrative bout in boxing history.
While Pacquiao appeared to be more eager for the fight when the two first began verbally sparring in 2009, Mayweather has taken the lead in recent months, stepping up his campaign since Pacquiao's narrow win over Juan Manuel Marquez last November.
Mayweather's tweets appear to put the megafight's future in Pacquiao's hands — and a decision likely will be made soon.
Top Rank promoter Bob Arum travelled to the Philippines this week to meet with Pacquiao, planning to choose the eight-division champion's next opponent. Arum, who has repeatedly said Mayweather won't actually agree to fight Pacquiao because he fears losing, has a list of candidates including Marquez, Miguel Cotto, Lamont Peterson and Timothy Bradley Jr. for Pacquiao's next bout.
Arum also has suggested Pacquiao might not be ready to prepare for a fight in May because of a facial cut from his win over Marquez. Mayweather's camp has dismissed that notion as subterfuge, saying cuts rarely require several months to heal.
Golden Boy Promotions CEO Richard Schaefer, whose company has promoted Mayweather's last five fights, has suggested Mayweather's Cinco de Mayo fight could be against popular 154-pound Mexican champion Saul (Canelo) Alvarez or lightweight champion Robert Guerrero, a Mexican-American from the Bay Area, if he can't make a deal with Pacquiao.
But if Mayweather and Pacquiao intend to make their long-awaited fight, both sides know they must do it quickly, since a promotion of that size would require several months of preparation.
Mayweather controls his own Twitter feed, which is often filled with pictures of his fiancee and braggadocio about his gambling exploits. On Monday night, he tweeted a photo of a betting slip, claiming he won US$400,000 on the BCS title game.