CINCINNATI (AP) _ The last of four NBA referees indicted in an airline ticket scam pleaded guilty Friday to tax evasion.

Mike Mathis, 54, was charged with understating income by $69,000 from 1989 through 1992. He pleaded guilty in federal court to one count of filing a false tax return in 1992 and immediately resigned from the league.

``I thoroughly enjoyed my nearly 22 years of employment as a referee with the NBA,'' Mathis said in a statement released by his lawyer, Terrence Grady. ``And while I understand the difficult position the NBA is facing in this matter, it is my hope to resume my career with them at some point.''

The NBA did not immediately comment.

Mathis admitted trading in first-class airline tickets provided by the NBA for cheaper, coach-class tickets and pocketing the difference, authorities said. He did not report the extra income on his taxes.

U.S. District Judge Sandra Beckwith said she will wait for a report before sentencing Mathis, who faces up to five years in prison and a $250,000 fine. She did not set a sentencing date.

Mathis, of suburban Cincinnati, was indicted in 1997 along with three fellow referees: George Toliver of Harrisonburg, Va.; Jesse Kersey of Williamsburg, Va.; and Henry Clinger Armstrong of Virginia Beach, Va.

Under the referee's collective bargaining agreement with the NBA, the league was required to buy them to travel first class on plane trips longer than two hours.

Mathis admitted using several means to conceal income generated from downgrading seats, including obtaining bogus airline receipts and invoices from a travel agent in Denver.

Toliver and Kersey pleaded guilty to tax evasion, agreed to cooperate in the investigation and resigned from the NBA.

Armstrong pleaded guilty to tax evasion and is awaiting sentencing.

The indictments stemmed from a two-year Internal Revenue Service investigation.

``Here, a prominent and highly paid person welched on his legal obligation to pay his full share of taxes,'' U.S. Attorney Sharon Zealey said after Mathis made his plea.