Stunned passers-by watched as a scissors-wielding zealot slashed a billboard showing the Virgin Mary clutching a positive pregnancy test.
The grey-haired man appeared to be alone as he attacked the poster outside the St Matthew-in-the-City church in central Auckland before driving off.
Whangarei man Arthur Skinner, a member of the Catholic Action Group, later claimed responsibility for the incident.
He was believed to have earlier phoned St Matthew's vicar Glynn Cardy to say he would "roast slowly in hell" for erecting the billboard.
"He told me I would burn in the fires of hell, that would be my final destination," Cardy said.
Catholic Church spokesman Lyndsay Freer said she, too, had received an unhappy phone call from who she thought was Skinner about the poster.
The Catholic Action Group had "absolutely nothing" to do with the mainstream Catholic Church, she said. "I have been critical of the poster, but the last thing we would want to do would be anything destructive."
Last night, Radio Network aired a statement from Skinner inviting concerned people to join him outside the church at 11am and he would hold up the portion of the billboard for cameras and explain why the group did what it did. He said if he was arrested, so be it.
The contentious billboard has gained worldwide notoriety. Reports have appeared in newspapers as far afield as the New York Daily News and Britain's Daily Mail. A headline on US TV channel Fox News declared the billboard "sick".
"I'm a bit disappointed that those who think that any image that's not their image should be defaced or torn down as blasphemy," Cardy said. "But every faith has got fanatics."
The church's intention was to get people to think about Mary, he said. He denied it was deliberately provocative.
"There is nothing in this billboard that I don't believe in."
St Matthew's Facebook page has attracted dozens of comments. Lonnie Cooper wrote: "This image is horrific and shameful. If this happened in my parish, we would string our priest from the rafters in the Church."
Denny Lee, wrote: "If only I stayed in Auckland, I would attend to your church."
Catholic Action Group came to prominence in 2003 when it bombarded MPs with email warnings they would go to hell if they voted in favour of the Prostitution Reform Bill.
But neither is St Matthew's any stranger to controversy.
A billboard the church posted at Christmas two years ago showed Mary and Joseph in bed, with the caption: "Poor Joseph. God was a hard act to follow."
It provoked such anger that it was taken down.