The 30-year-old star - who plays practical jokes on fellow celebrities for his MTV show 'Punk'd' - won't target his colleagues because he is afraid of being blacklisted in Hollywood.
He said: "If you punk your co-stars, people don't want to work with you any more. So I don't do it, it's that simple."
Cameron Diaz, who stars alongside Ashton in new comedy 'What Happens in Vegas', believes Ashton is right to have a no co-star rule.
She said: "The biggest thing when you're working together is trust. That can't work if you think that around every corner you're going to get slapped in the face."
Last week, Cameron revealed she put on a special screening of 'What Happens in Vegas' to help her family grieve the loss of her father Emilio Diaz, who died of pneumonia in April.
She said: "It was a unanimous decision that we all needed to share a good laugh. After all that's why we make films like these. So people can leave behind their worries for a couple of hours. Have a good laugh."
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