Failure to do so is considered an offence, and can incur a fine of up to $40,000.
Dunedin National MP Michael Woodhouse said besides being factually incorrect, the advertising was clearly not National's, not authorised and therefore in breach of the Electoral Finance Act 2007.
"I don't know who did this, but it is a bit disappointing. But I think people will realise what this is, and know what to do with it, so I'm not giving it too much time."
It was likely a complaint would be laid with the commission, although he acknowledged as the flyer was anonymous, it would be difficult for the commission to investigate.
Meanwhile Labour leader Phil Goff is standing by a mailed leaflet telling mothers on a benefit they "won't be around to celebrate" their child's first birthday if National wins the election.
The leaflet, which was sent nationwide, aims to highlight National's welfare reforms, in particular the proposal to work-test sole parents who have more children while on a benefit.
Mr Goff says the 'hard-hitting' pamphlet is not misleading.