Manny Pacquiao has promised to take legal action following a row over blood-testing which is threatening his planned fight with Floyd Mayweather.
Pacquiao has refused to submit to blood-testing in the 30 days leading up to the fight which has been scheduled for March 13 but is now in doubt.
The Mayweather camp have insisted on both fighters making themselves available for testing, in accordance with US Anti Doping Agency regulations, to ensure they are clean.
The welterweight super-fight in Las Vegas was set to earn each fighter huge purses but may now not happen.
Pacquiao insists he has never used any drugs and his trainer, Freddie Roach, has condemned the opposition camp's demands for heightened levels of testing, stating: "We have passed every test ever given to us. We go by the commission rules, since when does the fighter make up the rules?"
Floyd Mayweather Sr, the trainer, said earlier this year he believed Pacquiao was 'on some type of supplements'.
Mayweather Jr said this week that Pacquiao's refusal to undergo blood-testing as requested 'leaves me with great doubt as to the level of fairness I would be facing in the ring that night'.
Now Filipino fighter Pacquiao has said in a statement: "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 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 I have cheated my way into becoming the No.1 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."
Pacquiao's statement added: "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."
"Pretty Boy Floyd, face me instead on March 13 in Las Vegas and not in some talk show forum or in press releases written for you by people who don't even know me. Face me in a fight where I get to punch back. You and your cohorts have accused me of using performance-enhancing drugs. Now, I say, the burden of proof should now come from you, not me."