The television cartoon show of a Virgin Mary statue bleeding will go to air despite Catholic bishops urging their congregations to boycott TV3's news and advertisers.

Responding to an open letter from Catholic bishops, the chief of TV3 and sister channel C4 said if Catholics feared they might be offended by the "Bloody Mary" episode of the South Park show, they should switch it off.

"We absolutely expect there's segments of society that would be offended by the programme," said Rick Friesen, chief operating officer of CanWest-owned TV Works.

The bishops yesterday circulated a letter that was read at Masses and is published on the church's website decrying South Park's "ugly and tasteless" depiction of Mary, the mother of Christ, who is revered in Catholicism.

The episode shows a statue of Mary bleeding, which is taken to be a miracle, until Pope Benedict suggests it is simply menstruation. The statue then starts spurting blood.

The seven bishops' pastoral letter says the programme is demeaning of Mary and women in general.

It also suggests protesting against the "insults" by boycotting TV3 news and products advertised on TV3 and C4 - and telling TV3 and the advertisers why.

Auckland Bishop Patrick Dunn said he would stop watching TV3 news if C4 went ahead with the programme.

The bishops' letter follows one last month by Catholic and other religious leaders, including Jewish organisations and the Council of Christians and Muslims, to TV Works complaining about "Bloody Mary".

The "scurrilous" programme would give "grievous and gratuitous offence" to many.

"Mary is honoured and commemorated by millions of Christians, including Catholics, and is respected also by people of other faiths," the letter said.

In the United States, Comedy Central screened the episode once last year but pulled a repeat after pressure from a Catholic group.

Mr Friesen said it was no "edgier" than usual for South Park, which was a satire. "C4 viewers expect an edgier channel. They expect C4 to go a little beyond what TV3 would. They would be pretty disappointed in C4 and the brand if we didn't run it."

It was "definitely" a press-freedom issue, he said. "We definitely decide what will run on the channel.

"We absolutely want to respond to viewers, but don't want to be overly responsive to pressure groups."

He denied any parallel to the debate over the publication and broadcast by news media of cartoons featuring the Prophet Muhammad, one of which showed him wearing a bomb-like turban - an act which prompted widespread protests from Muslims and violence overseas.

"All this is a depiction of a statue of the Virgin Mary, commonly seen in churches," Mr Friesen said. He did not mention the spurting blood.

In reaction, Prime Minister Helen Clark said: "We respect the right of media to free speech, but it is a matter of taste and judgment and we hope they take care to show respect to all cultures and faiths."

Race Relations Commissioner Joris de Bres, who brought together Muslims, media and others to help settle the row over the Muhammad cartoons in New Zealand, yesterday urged CanWest to consider the submissions of those who objected to the South Park episode.

He said he generally did not comment on such issues, but he drew a distinction between news media, in which readers and viewers had little choice in their sources, and entertainment, where the choice was wider.

Parishioners at evening Mass at St Benedict's in Newton believed C4 should not broadcast the episode.

Consultant Michael Hart thought the episode insulted Christians and likened it to the caricatures of the Prophet Muhammad.

"I think newspapers and television should be more attentive to the thoughts and feelings of people."

Regular South Park watcher Simon Dennerly said he would stop watching the programme. "It's clever stuff, but if they keep at it, why should I?"

Elly Blackwell said it was just one more in a series of high-profile insults to Catholics - another being the Te Papa exhibit Virgin in a Condom. "Now this, what's next?"

The episode will screen on May 10.