The Electoral Commission is investigating claims an Auckland man stole hundreds of flag voting papers and voted in favour of the new design.
Several people alerted the commission to the comment he made on a Facebook page five days ago.
The man wrote that he had collected nearly 300 voting papers from neighbours and friends that he believed "couldn't care less".
He had ticked the new flag option on all of them - but it was not known if the papers have been cast.
The man said no referendum has ever brought change except for the Irish referendum that allowed gay marriage.
The Electoral Commission has referred four incidents of alleged flag referendum misconduct, posted on social media, to the police.
Several of the 20 complaints it has received relate to the Auckland incident.
A person who is convicted of filling out someone else's voting paper faces a maximum sentence of two years' jail and or a fine of up to $40,000.