Mayweather Jr and Pacquaio would have earned millions from the fight
Manny Pacquiao has launched legal proceedings against Floyd Mayweather for accusing him of taking performance-enhancing drugs.
The Filipino pulled out of a lucrative fight to face Mayweather on 13 March after the American demanded Olympic-style drugs tests ahead of the bout.
The lawsuit filed in a Las Vegas court names Mayweather's father, uncle and Golden Boy Promotions.
Oscar de la Hoya, founder of Golden Boy, is also mentioned.
The lawsuit claims the Mayweathers, six-weight world champion De la Hoya, and Golden Boy Promotions chief executive Richard Schaefer knew that WBO welterweight champion Pacquaio has never taken performance-enhancing drugs and made their statements out of "ill-will, spite, malice, revenge, and envy".
Pacquaio's lawyer Daniel Petrocelli said: "Manny's achievements come from God-given talent and an indefatigable work ethic - not steroids.
"He cannot and will not allow others to deliberately misrepresent his years of hard work and tarnish his reputation."
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
Pacquaio withdrew from what was expected to be the richest fight in boxing history last week following a disagreement about blood tests 30 days prior to the fight.
The Filipino said he would only give blood before the initial media conference and immediately after the fight.
Although Pacquaio said he would agree to testing by the same agencies that conduct tests for pro American Football and baseball players, he would not sign up to random tests by the US Anti-Doping Agency.
Promoter Bob Arum accused Mayweather's camp of raising the issue not because they were worried about Pacquiao taking performance-enhancing substances, but because Mayweather Jr never wanted to fight in the first place.
Pacquaio signalled his intentions to take matters into the court room on Christmas Day.
"I have instructed my promoter, Bob Arum, to help me out in the filing of the case as soon as possible," said the 31-year-old, who has never tested positive for performance-enhancing substances.
"Enough is enough. These people, Mayweather Sr, 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.
"I have tried to just brush it off as a mere pre-fight ploy but I think they have gone overboard.
"I have had people coming over to me now asking if I really take performance-enhancing drugs and I have cheated my way into becoming the number one boxer in the world,"
"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.
"Now, I say to Floyd Mayweather Jr, don't be a coward and face me in the ring, mano-a-mano and shut your big, pretty mouth so we can show the world who is the true king of the ring."
Mayweather's team tried to diffuse the issue in a statement last week.
It read: "Let it be very clear that nobody from Team Mayweather or Golden Boy Promotions is accusing Pacquiao of anything.
"But the reality seems to be that, for whatever reason, Pacquiao does not want to participate in random blood testing, which has already been deemed a harmless procedure that many current athletes are subjected to, prior to and during competition."
Unbeaten Mayweather and five-weight champion Pacquaio - considered to be the best pound-for-pound boxers in the world - were set to meet at the MGM Grand Garden Arena in Las Vegas in the biggest fight since the turn of the century.
Pacquiao became a five-weight world champion following his WBO welterweight title win over Miguel Cotto in November, while Nevada-based Mayweather returned from a 21-month retirement to beat Mexican Juan Manuel Marquez in September.