New York ? David Stern led the NBA through drug problems and work stoppages. Now his league faces the stigma of a point-shaving scandal involving a referee.

The NBA acknowledged Friday that the FBI is investigating Tim Donaghy for betting on games, including ones in which he officiated.

According to a law enforcement official, authorities are examining whether the referee made calls to affect the point spread in games on which he or associates had wagered over the past two seasons.

The referee had a gambling problem and was approached by low-level mob associates through an acquaintance, said the official, who spoke to the AP on condition of anonymity.

Donaghy is perhaps best-known previously as one of the referees in the 2004 game at Detroit that ended with Indiana Pacers players fighting with Pistons fans, among the biggest black marks in league history.

This could top it.

“We would like to assure our fans that no amount of effort, time or personnel is being spared to assist in this investigation, to bring to justice an individual who has betrayed the most sacred trust in professional sports, and to take the necessary steps to protect against this ever happening again,” Stern said in a statement.

Donaghy officiated 68 games in the 2005-06 season and 63 games in 2006-07, according to the Elias Sports Bureau. He also worked 20 playoff games, including five last season – Pistons-Magic on April 23; Warriors-Mavericks on April 27; Suns-Lakers on April 29; Nets-Raptors on May 4; and Spurs-Suns on May 12.

The National Basketball Referees Association did not return calls for a statement, and Donaghy reportedly has resigned from the league.

A woman came to the door of the Bradenton, Fla., home where Donaghy lives and shouted through the door: “We have no comment.”

Defense attorney John Lauro confirmed Donaghy is under investigation but refused to comment on the allegations or the case.

Stern’s statement said the FBI is investigating allegations a “single” referee bet on basketball. But the law enforcement official, who requested anonymity because he was not authorized to discuss the ongoing case, said other arrests are expected.

Those studying Donaghy’s games might have noticed some trends.

When the home team was favored by 0-41â2 points, it went 5-12 against the spread in games officiated by Donaghy this season, according to Covers.com, a Web site that tracks referee trends. Home underdogs were 1-7 against the spread when it was 5-9.5 points.