What began as an apparent simple disagreement between the camps of Manny Pacquiao and Floyd Mayweather Jr. over how to handle drug testing for their megafight -- tentatively scheduled for March 13 at the MGM Grand in Las Vegas -- has spiraled so out of control that the potential biggest money fight in boxing history was in serious jeopardy on Christmas Day.

Pacquiao, angered by accusations from the Mayweather camp that he uses performance-enhancing drugs, said he would file a defamation lawsuit against Mayweather and Golden Boy Promotions.

"Enough is enough. These people, Mayweather Sr., [Mayweather] Jr. and Golden Boy Promotions, think it is a joke and a right to accuse someone wrongly of using steroids or other performance-enhancing drugs," said Pacquiao, who denied that he has ever used any banned substance and who has passed all of his drug tests. "I have tried to just brush it off as a mere prefight ploy, but I think they have gone overboard."

Floyd Mayweather Sr., the fighter's father, has repeatedly accused Pacquiao of taking illegal substances and points to his rising through weight divisions to win titles in a record seven divisions while maintaining his speed and power.

"I have instructed my promoter, Bob Arum, head of Top Rank Inc., to help me out in the filing of the case as soon as possible because I have had people coming over to me now asking if I really take performance-enhancing drugs and [if] I have cheated my way into becoming the No. 1 boxer in the world," Pacquiao said.

"I maintain and assure everyone that I have not used any form or kind of steroids and that my way to the top is a result of hard work, hard work, hard work and a lot of blood spilled from my past battles in the ring, not outside of it. I have no idea what steroids look like, and my fear in God has kept me safe and victorious through all these years."

Arum was making plans for an alternative bout for Pacquiao to defend his welterweight title on March 13 against former junior welterweight titlist Paulie Malignaggi, in the event the fight with Mayweather can't be finalized.

"I reached out to Lou DiBella [Malignaggi's promoter], and we're going to schedule that fight for March 13 unless something drastically changes with this Mayweather thing," Arum told ESPN.com on Friday, just before leaving for a working vacation in Cabo San Lucas, Mexico. "I'm not going to leave Manny without a fight because of this nonsense [with Mayweather]."

Ironically, Malignaggi also has repeatedly accused Pacquiao of using PEDs.

A plan proposed by HBO to have Sen. John McCain, a serious boxing fan, mediate the drug-testing dispute was originally embraced by the camps but was later shot down by Pacquiao. Arum then suggested that the Nevada State Athletic Commission oversee the testing.

"Manny is pissed off, but I think I can bring him back into the fight by having Nevada do it," Arum said. "He's fought in Las Vegas many times and is comfortable with the people on the commission."

Mayweather is demanding Olympic-style testing conducted by the U.S. Anti-Doping Agency, whose inflexible protocol calls for random urine and blood testing throughout training camps, fight week and even the day of the fight, with the ability to test any time, day or night. Both fighters would be subject to the same kind of testing.

The Pacquiao camp originally suggested using the more flexible agencies that oversee testing for American professional sports leagues before Arum said testing should be overseen by the Nevada commission.