Former Alliance Party organiser Matt McCarten is standing in the Mana by-election.
Mr McCarten, who is standing as an independent, is the general secretary of Unite, the union which represents low-paid workers.
He joins Labour Party candidate Kris Faafoi, National Party list MP Hekia Parata and Green Party candidate Jan Logie in contesting the seat which had been held by Labour's Winnie Laban.
Nominations for the seat close on Wednesday afternoon when the Electoral Commission is expected to release the full list of candidates.
