Christian groups have condemned a provocative Spanish play about Jesus called Golgota Picnic (Golgotha Picnic), due to premiere in France.
Street protests are planned when the play is performed in the southern city of Toulouse, before moving on to the capital Paris.
While urging restraint, Toulouse's Catholic archbishop said the play "fouled the faith of many believers".
Its Argentine-born author said he found it "healthy" when people took a stand.
The theatre's manager, Jacky Ohayon, insisted Rodrigo Garcia's play was not blasphemous and pointed out it had run for six months in the Spanish capital Madrid "with no trouble".
Christian fundamentalists are expected to protest publicly outside the Garonne Theatre in Toulouse on Wednesday, while a counter-demonstration in support of freedom of speech is being organised by leftist groups.
CRS riot police have reportedly been put on stand-by.
Last month, a similar demonstration in Paris "against Christianophobia" gathered about 1,000 people.
'Christ as madman'
In a message carried by the Toulouse diocesan website, Archbishop Monsignor Robert Le Gall said: "Mr Rodrigo Garcia wants to denounce forcefully all forms of fundamentalism and rebel against an all-powerful God he has feared since childhood - that is not the God Christians proclaim...
"Is it right to foul the faith of many believers, to attack them in their devotion to Christ? I do not think so."
But the archbishop warned protesters to be wary of being "manipulated by fundamentalists and political groups", and condemned any use of violence.
He distanced the Church from activists who had, he said, been distributing leaflets outside Toulouse churches.
Another senior Catholic cleric, Bishop Dominique Rey of Frejus-Toulon, condemned what he said was Garcia's depiction of Christ as "madman, dog, pyromaniac, messiah of Aids, devil-whore, no better than a terrorist".
Garcia himself said his play, which depicts the life of Christ through shocking images of contemporary consumer society, was a reflection of everyday reality.
"I find it healthy to see people take a stand and say they don't like it, even if what I show is only a reflection of what is in front of our eyes every day but nobody chooses to see," he was quoted as saying in France's La Depeche newspaper.
A bid by Catholic groups to have the play banned was rejected by the regional authorities in Toulouse.