It was reported last month that the actress was irritated by Vaughn's 'relaxed' attitude during filming of romantic comedy Four Christmases.
Sources claimed that Vaughn regularly turned up on set looking like he had been out all night and that he preferred ad-libbing to rehearsing with his co-star.
The Oscar-winning actress is now rumoured to have rebelled at the prospect of filming an intimate love scene with Vaughn.
An insider told the New York Post: "Reese has an issue with the scripted love scene. It is meant to be a funny, American Pie-style romp, full of bumps and laughs, but Reese is of such a prude, she thinks it's just too much."
Vaughn is one of the producers of the movie, which is scheduled for release next Christmas.