So says The Smoking Gun:

A lengthy investigation by The Smoking Gun has uncovered remarkable details about Sharpton’s past work as an informant for a joint organized crime task force comprised of FBI agents and NYPD detectives, as well as his dealings with an assortment of wiseguys.

Beginning in the mid-1980s and spanning several years, Sharpton’s cooperation was fraught with danger since the FBI’s principal targets were leaders of the Genovese crime family, the country’s largest and most feared Mafia outfit. In addition to aiding the FBI/NYPD task force, which was known as the “Genovese squad,” Sharpton’s cooperation extended to several other investigative agencies.

Sharpton has flatly denied most of the allegations in The Smoking Gun's story, although: "When asked specifically about his recording of the Gambino crime family member, Sharpton was noncommittal: 'I’m not saying yes, I’m not saying no.'"