The IRS says boxer Floyd Mayweather owes $US22 million (NZ$30.45m) in taxes from 2015, the year he earned his biggest payday with a blockbuster fight against Manny Pacquiao.
A notice of a federal tax lien filed against the undefeated fighter nicknamed "Money" shows the balance as unpaid as of March 6.
The document was filed with county officials in Las Vegas in April.
Mayweather's tax troubles come as he gets ready to come out of retirement to fight against Irish MMA star Conor McGregor in August.
The lien for 2015 is just the latest in a series of tax liens filed by the IRS against Mayweather over the past decade.
Mayweather's tax lawyer did not immediately return a request seeking comment on Tuesday.
Mayweather appeared at a news conference in Los Angeles on Tuesday (Wednesday NZ time) to promote the fight, the first of four this week.
He said in a Facebook post that he paid the IRS $US26 million in 2015, and that he's sure he would have been notified much sooner had there been any "real discrepancies."
Mayweather said: "My empire is rock solid and intact."