This movie was supposedly based around the life of Joey Gallo, a New York gang leader. Word has it that the members of Gallo's crew wished to seek vengance on the writers.
While Paramount brass dithered over whether to cast him as Michael Corleone, the role that would make him a star, a frustrated Al Pacino signed up for the role of Mario Trantino in this movie. When Paramount decided to offer him the role, they had to buy him out of his contract with Metro-Goldwyn-Mayer. Ironically, the role went to Robert DeNiro, whom "The Godfather Part II" would make a star.