Katherine Heigl has been branded a "difficult" actress.

The former 'Greys Anatomy' star allegedly caused "desperately difficult situations" on the set of her 2010 movie 'Life As We Know It', in which she starred opposite Josh Duhamel, and has developed a bad reputation in Hollywood.

A source, who worked on the movie, told the Hollywood Reporter: "She can cost you time every single day of shooting. Wardrobe issues, not getting out of the trailer, questioning the script every single day."

The source said that the 34-year-old actress's mother and manager Nancy Heigl was even tougher to deal with during filming.

The insider said: "I have never experienced anything like Nancy Heigl. It's about the mouth. 'F**k you. You are a f**king liar.' Whatever you'd say, you were an idiot. The call would be, 'This is the worst craft service we've ever had! There's nothing to eat! This is the worst wardrobe!' You knew that every day, you were going to get slammed. The frustrating part is [Heigl] is incredibly talented and smart."

The movie's director Greg Berlanti dismissed the allegations, saying: "I would work with her (Katherine) again in a heartbeat."

Producer Denise Di Novi admitted that Katherine and her mother are both very strong women but insisted the claims were "way exaggerated."

She said: "(They) are not shrinking violets. They're very straightforward and tell you what they think."

But a source from the set of Katherine's 2008 movie '27 Dresses' backed up the accusations, saying: "There were movie-star demands -- big rooms, the mother there, all the stuff . . . It was just a sense of entitlement. The biggest stars don't do that kind of thing."

Katherine, who reportedly declined to comment on the accusations, is hoping to reignite her career by starring in a new NBC series about the CIA.