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.