Reese Witherspoon is refusing to film a sex scene with Vince Vaughn.

The pair have reportedly been clashing constantly on the set of romantic comedy 'Four Christmases' and now Reese is refusing to roll around naked with Vince.

An on-set source told the New York Post newspaper: "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 such a prude, she thinks it's just too much."

Despite being an Oscar winner and a more highly-paid Hollywood star, Reese is unlikely to win the argument as Vince is one of the film's producers.

The 37-year-old actor also oversaw much of the script writing, about a couple whose divorced parents do not get on, so they decide to celebrate Christmas separately with each of them.

It has previously been reported Reese, 31, has been unhappy with Vince's behavior on set.

While she is keen to work hard and film on schedule, he allegedly turns up to work hung-over, forgets his lines and is constantly fooling about on set.