A significant number of MPs will not vote in the smacking referendum, saying it is a "waste of time", a "waste of money" and the wording is "nonsensical".

In a Weekend Herald survey of 122 politicians, nearly half of the 62 who responded said they would not vote in the referendum and two planned to spoil their ballot papers in protest.

Prime Minister John Key and Labour leader Phil Goff had earlier announced they would not vote because the wording of the question was too ambiguous.

Most of the 25 MPs following suit also said they were unhappy at the "ambiguous" nature of the wording.

Others were not voting because they believed it was a chance for the public to have their say on their issue - not MPs.

Other than the Act MPs - who have opposed the changes to section 59 from the start - only two others openly said they would vote "no" - National's Tim Macindoe and Cam Calder.

Mr Calder said he was voting "no" on the literal wording of the referendum, rather than because he thought the current law was not working.

"I do not believe a light tap with a finger by a parent should render that parent liable to prosecution. But with the law as it stands, I haven't heard of anybody being prosecuted for that."

Many of those not voting at all said they did not believe the law should change again. National's Judith Collins believed it was being applied correctly.

"I think it doesn't need to change, so I don't think the question is fair enough."

Some were effectively boycotting the referendum because of the wording.

New National MP Nikki Kaye said she could not comfortably vote on the question.

"My worry is that many people I talk to see a 'yes' vote as a vote to reduce family violence and a 'no' vote as a vote to stop the Government interfering and telling them how to bring up their kids. I believe in reducing family violence and Government interference in people's lives."

Labour's Chris Hipkins faced a similar problem.

"I will probably vote but haven't decided how to vote yet. I don't want good parents to feel like criminals but nor do I condone thrashing kids. I think the current law is working."

Labour's Rajen Prasad - who headed the Families Commission when the law change went through in 2007 - said he could not vote either way with comfort, so he planned to spoil his ballot paper.

Jim Anderton - a "yes" voter - also intended to make a point by writing his disapproval of the wording on the envelope used to post the vote.

Even Chester Borrows - who had supported the petition to force the referendum before the compromise law was passed in 2007 - said he would not vote and did not believe the law should be changed.

National: David Bennett, Jackie Blue, Chester Borrows, David Carter, Judith Collins, Chris Finlayson, Tim Groser, Nathan Guy, Tau Henare, Steven Joyce, Nikki Kaye, John Key, Todd McClay, Tony Ryall, Katrina Shanks, Nick Smith, Anne Tolley, Chris Tremain, Louise Upston, Michael Woodhouse.

Maori Party: Tariana Turia.

Labour: Phil Goff, Annette King, Trevor Mallard, Damien O'Connor.

* Spoiling ballot paper: Clayton Cosgrove, Rajen Prasad.

Labour: Steve Chadwick, Charles Chauvel, Kelvin Davis, Darien Fenton, Parekura Horomia, Moana Mackey, Su'a William Sio, Maryan Street. Progressives: Jim Anderton.

United Future: Peter Dunne.

Green Party: Sue Bradford, Keith Locke, Kennedy Graham, Metiria Turei, Russel Norman, Jeanette Fitzsimons, Sue Kedgley, Kevin Hague, Catherine Delahunty.

Maori Party: Te Ururoa Flavell (if votes), Hone Harawira, Rahui Katene.

National: Cam Calder, Tim Macindoe.

Act: John Boscawen, David Garrett, Heather Roy.