Disney says the character in its new Lone Ranger film is "a ruthless outlaw whose terribly scarred face is a perfect reflection of the bottomless pit that passes for his soul".
But the Cleft Lip & Palate Association of Ireland (CLAPAI) has warned parents of children with the condition to be prepared for the release of the movie.
It is due out here on August 9 with a 12a cert, but has already bombed in the US.
Lego brought out a range of toys to accompany the movie and it includes the character Butch Cavendish, complete with cleft lip.
CLAPAI chair Georgina Wade said: "The issue is not that a movie character has a cleft lip or that Lego has duplicated the cleft.
"The issue is the deliberate negative association of a cleft. The ideology and wording are extremely offensive to people living with cleft and their family and friends.
"There is no doubt that this is what the movie sets out to do. William Fichtner, the actor who plays the villain, says when asked about acting under the make-up: 'You know, I have the prosthetic broken nose, the whole cleft lip ...'
"This association of a cleft lip with evil may lead to bullying, mocking and an expectation that children with a cleft should be the bad guys in playground games."
Disney had not replied to the CLAPAI statement at the time of going to press.
Cleft lip is one of the most common congenital facial conditions worldwide: in Ireland, between 100 and 120 babies are born with it every year.
The CLAPAI said Disney's "unnecessary portrayal implants an incorrect psychological connection between cleft and evil".