From New York Post:
Steve Schirripa, who portrayed Bobby Baccalieri, recently spoke about a moment during filming where Gandolfini and Michael Imperioli got so drunk before shooting a scene that they had to be chained to a tree.
“On the break, while they set up the lights, Michael and Jim [Gandolfini] drank a bottle of Wild Turkey,” Schirripa told Insider. “They were so drunk that they had to chain their legs to a tree, because they were afraid they were going to fall off the cliff,” Schirripa added.
The scene in question was the moment in Season 4, where Tony and Christopher Moltisanti (played by Imperioli) threw the body of Ralphie Cifaretto (Joe Pantoliano) off a cliff.