The Electoral Commission has referred Mediaworks to police after a broadcaster on George FM urged people to vote for the Green Party on election day.
The commission said the Auckland-based station broadcast statements on September 20 which were intended to influence people how to vote before the polling booths closed - a breach of electoral rules.
In a statement, the commission said it also took the view that the short broadcast by George FM was an election programme, which was a breach of the Broadcasting Act.
A Mediaworks spokeswoman said the company took its responsibilities as a broadcaster seriously, and trained its staff about election day rules.
"Unfortunately on Saturday 20th September, one of the announcers on George FM was a volunteer, and was unaware of their responsibilities under the Electoral Act."
At 4.50pm on election day, the volunteer said on air that he had voted for the Greens and encouraged listeners to do the same and vote out the National-led Government.
The Electoral Act forbids supporting or criticising any party or candidate on election day before 7pm.
Mediaworks said it was now reviewing its policy on whether it used volunteers on air on voting day.
If police decided to prosecute, the company was liable for a maximum fine of $20,000 for breaking electoral rules, or $100,000 for breaking broadcasting laws.
Prosecutions for similar breaches were rare.
George FM was one of a handful of individuals or organisations who had been referred to police by the commission.
Among them were the Avonhead Community Group, who distributed a leaflet which promoted a candidate without authorisation and without a promoter statement.
Aotearoa Legalise Cannabis Party candidate Robert Wilkinson was referred to police for distributing a letter without authorisation.
And sports stars Israel Dagg, Jonah Lomu, Eric Murray and Hamish Watson were all being investigated for sending tweets in support of National and John Key on election day.
Electoral Commission head Robert Peden said on Saturday that some electoral rules may need to be reviewed, including those which cover social media.
Rules around advertising during the election campaign may also have to be reviewed in light of the massive increase in advance voting, which doubled between 2011 and 2014.