The Labour Party says its odds in the Mana by-election might have narrowed after the head of the Unite union, Matt McCarten, put his name forward to contest the seat.
Mr McCarten says the executive of his union, which represents low paid workers, asked him to stand and he wants to base his campaign around Unite's push for a minimum wage of $15 an hour.
His last-minute entry has added interest to the campaign which had largely pitted Labour's Kris Faafoi against National list MP Hekia Parata, Radio New Zealand's political editor says.
Matt McCarten dismisses suggestions he might split Labour's vote, saying if that was a concern to the major parties then elections might as well be called off.
Labour Party leader Phil Goff says Mr McCarten is more likely to take voters from the Green and Maori parties.
Nominations for the by-election closed on Wednesday and voters got to the polls on 20 November.