Most of New Zealand's mainstream churches are supporting a "Yes" vote in the referendum on whether smacking should be a criminal offence.

The heads of the Anglican and Methodist churches say the current law, which bans the use of force against children for "correction", is working well and should not be changed.

The Catholic Bishops Conference referred questions to the church aid agency, Caritas, which recommended a "Yes" vote on the basis that the current law was close to the compromise which the bishops sought in 2007 between a complete ban on physical restraint and allowing "violent" discipline.

"The Catholic bishops have clearly recognised in several statements now the importance of facing up to our responsibility to better protect children," said spokeswoman Lisa Beech.

She said they also believed in the "subsidiarity" of families, meaning that the state should not interfere with decisions that families could make for themselves.

"That meant defining a threshold for protection," Ms Beech said. "The law isn't perfect, but we are reasonably satisfied with the compromise."

The churches' views are in contrast to the prominence of grassroots Christians in the campaign for a "No" vote in the referendum, which has been endorsed by Christian groups such as Focus on the Family and Sully Paea's Otara-based Crosspower Ministry.

Even conservative churches, while not quite urging a "Yes" vote, say the current law is working.

Baptist national leader Rodney Macann said the referendum was an opportunity for churches to declare their belief in "zero tolerance for violence".

"No one believes that correction should be a criminal offence, and that's not the way it's being dealt with by the police," he said.

Presbyterian Moderator Graham Redding said his church did not have a position on the issue. Anglican Archbishop David Moxon said the Anglican Church supported the 2007 law change which removed parental correction as a defence against a charge of assaulting a child, and stood by the law.

Methodist Church president Jill van de Geer and vice-president Ron Gibson have sent a pastoral letter to churches saying the 2007 law "at last gave children equal rights in our community with other people".

"There is no evidence to suggest that innocent people are being prosecuted and we feel to repeal this law would be a retrograde step," they said. Jill van de Geer said yesterday that she supported a "Yes" vote, but advised people who felt they could not vote either "Yes" or "No" to cross out both options and send in invalid votes so that the result would show how they felt.

"That's better than silence, which couldn't be interpreted at all," she said.