Prime Minister John Key says the law on smacking is working but should that change results of a referendum would be considered.

A 2007 change to the Crimes Act made it illegal for parents to use force against children for "correction", but also allowed police the discretion not to prosecute "inconsequential" cases.

Opponents forced a referendum which asks: "Should a smack as part of good parental correction be a criminal offence in New Zealand?"

The postal ballot closes on August 21.

The referendum has been criticised as being confusing as some people who support the status quo may think that is what they are voting for if they tick no.

The Government believes the law is working as intended and police are only prosecuting serious cases.

A TV One News Colmar Brunton poll last night found 83 per cent will vote no.

Mr Key said while the law technically said smacking was illegal that was not how it was being administered.

Six monthly police reviews showed it was working well.

"I've always argued that if the law doesn't work we will change it. If an overwhelming bulk of New Zealanders vote no then what that should do, I think, is give Parliament the strength of courage to change the law if it starts not working," he told Newstalk ZB.

Mr Key said the Government had other priorities.

"We have a Parliament that has a certain number of sitting days, we have a law that at this point no one has been prosecuted under, the country also needs to decide what do they want me and the Government focused on," he told Breakfast on TV One.

"I personally think it's the recession."

Social Development Minister Paula Bennett yesterday said she would not be voting, preferring to hear the public's view.

Mr Key and Labour leader Phil Goff had already said they would not vote.