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

Donaghy will reportedly surrender to the FBI to face charges that he conspired to make calls that would affect the point spread of games. The referee had a gambling problem and was approached by low-level mob associates through an acquaintance, said the law enforcement source, who spoke on condition of anonymity. The NBA referees’ union didn’t return calls for a statement, and Donaghy reportedly has resigned. 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.