Seven cases of people voting twice in the flag referendum have been referred to the police by the Electoral Commission.
The cases of apparent dual voting are offences under the Flag Referendums Act and carry a maximum penalty of two years' imprisonment or a $40,000 fine.
The commission said it could not say where the alleged dual votes were cast from, or if any of them were connected.
Wellington lawyer Graeme Edgeler, who specialises in electoral law, said the most likely scenario was people filling in someone else's voting forms if they were sent to an old address.
Mr Edgeler said if the intended recipient then requested new voting forms and returned them, it would appear they had voted twice.
About 1.5 million people voted in the first referendum, or just under half of all eligible voters.
The winning "Silver Fern (Black, White and Blue)" flag, designed by Kyle Lockwood, will be put against the existing New Zealand flag in a second referendum in March.