Both sides of the smacking debate are slapping cash on advertising but hope they have avoided breaching spending rules.
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 Friday with early results expected that evening and final results on Tuesday.
There is a $20,000 maximum fine for breaching the $50,000 limit on each side of the campaign around a citizen-initiated referendum, which covers the full year up to the close of voting.
Today The New Zealand Herald reported that the initiator of petitions to hold the referendum, Kiwi Party leader Larry Baldock had spent the maximum $50,000 on a radio advertising campaign.
He said the spending was unrelated to the Vote No campaign.
Green MP Sue Bradford, whose member's bill sparked the law change, said her party's leaflet about why its MPs were voting yes was not part of the Yes Vote campaign.
Meanwhile, Vote No member Family First spokesman Bob McCoskrie said much of his party's annual budget of up to $250,000 was spent on advertisements about the smacking law but he said most was not related to the referendum.
Yes Vote spokeswoman Deborah Morris-Travers said her coalition had taken advice from the Chief Electoral Office and had been careful to keep within the $50,000 limit.
Chief Electoral Officer Robert Peden declined to comment on what either side was doing until their expense returns were filed by September 25.
"The expenditure limit applies to advertising which is used, or appears to be being used, to promote one of the answers to the referendum question, and is published or broadcast during the period from August 26, 2008, to August 21, 2009.
"It is an offence for any person, either alone or in combination with others, to knowingly spend more than the $50,000 expenditure limit."
NZPA