Leading UK Catholics and members of Opus Dei have formed a group to respond to the negative impact the Da Vinci Code film is expected to bring.
The film will be premiered at the Cannes Film Festival on 17 May
The Da Vinci Code Response Group, which also includes a Benedictine abbot and two priests, has condemned Dan Brown's book as "fiction trading as fact".
The group criticised its "damaging and grotesque" account of their faith.
The comments come just weeks before the film version of the novel, starring Tom Hanks, is due to be released.
The book, which has sold 40 millions copies worldwide, has been attacked for portraying the Catholic Church as a shadowy organisation that has spent 2,000 years covering up Christ's bloodline.
The response group is being co-ordinated by Austen Ivereigh, the director for public affairs of Cardinal Cormac Murphy-O'Connor, the Archbishop of Westminster and head of the Catholic Church in England and Wales.
In a statement the group said: "We believe the Da Vinci Code is fun and harmless in so far as it is treated as fiction. We do not believe in condemnations, boycotts or protests.
"Prickliness on the part of Christians leads us into the trap laid by Dan Brown - that the church is on the defensive because it is engaged in a cover-up.
"But we are also exasperated that many people without a good understanding of the Catholic Church and its history have been understandably deceived by Dan Brown's claim that the Da Vinci Code is based on facts and respectable theories.
"That deception is likely to be reinforced by the film because images are much more powerful than words."
Opus Dei, a conservative Catholic group with 86,000 members worldwide, are particularly angry about their order being portrayed as murderous and power-crazed.
The organisation has arranged special information evenings in London for the public and has asked Sony Pictures, which produced the new film, to include a caption explaining the film is fiction.
Sony has previously declined to reveal whether the film would carry such a disclaimer.
Opus Dei's communications director Jack Valero said he believed it was important to make it clear.
"The book is obviously trying to present fictional things as factual, and trying to deceive people in that way," he said.
"That's why Opus Dei asked for a disclaimer at the beginning of the film just to say this is pure fiction, and then that's fine, you can say what you like.
"But if you're trying to get people to believe it's fact when in fact it's fiction, then that's cheating really."
The film will premiere on 17 May at the Cannes Film Festival before going on general release worldwide on 19 May.