Boxing champion Floyd Mayweather is expected to earn over $100 million next month when he fights Irish mixed martial artist Conor McGregor, but he's fuming that he's on the hook for back taxes to the IRS.

Ahead of a press conference between the two trash talking fighters, news reports surfaced that Mayweather owes over $22 million in back taxes from 2015, when he had his last "super fight" against Manny Pacquiao, for which he earned an estimated $200 million. During the press conference, McGregor seized on the news, taunting Mayweather for his choice of attire. "He's in a fucking track suit!" McGregor said. "He can't even afford a suit anymore!"

Mayweather, who uses the nickname "money" due to his massive paydays, responded on Instagram with a photo of stubs totaling $26 million on checks appearing to be made out to the U.S. Treasury Department.

"Uncle Sam, received $26,000,000.00 from me in 2015!" he wrote. "What else could they possibly want? I'm sure I would have been notified much sooner if there were any real discrepancies right? Bottom line, everybody just wants to be a part of the 'Money May" show, including the IRS!"

Mayweather, who at 49-0 and is one of the most accomplished boxers of all time, is widely expected to have an easy time beating McGregor, because the event will be fought under boxing rules, and McGregor's professional career has been focused on MMA. Though McGregor has punching power, his lack of boxing background is likely to make it especially difficult to land blows against Mayweather, who is known for frustrating many opponents by his defensive skills that make him hard to hit squarely.