The National Party is considering going to the police and the Electoral Commission over damage to its billboards.
An unnamed group claims to have defaced 700 billboards, adding slogans on stickers including "The Rich Deserve More" and "Drill it! Mine it! Sell it!"
National Party president Peter Goodfellow says he has heard from a number of candidates in the Auckland area that this has been done to the billboards, but does not know how many have been defaced.
"Their billboards have been defaced with a number of slogans that have been plastered across them that are completely illegal because they're not authorised by anybody."
Mr Goodfellow says parties need to authorise every statement they make during an election campaign and National candidates have been going around peeling off the stickers from the billboards.
He says the defacing of the billboards was poorly executed and poorly thought out.
Mr Goodfellow says a conference is being held on Monday to discuss whether to lay a complaint.