Labour wants ACT leader John Banks stood down from his ministerial portfolios, in light of fresh allegations about donations to his mayoral campaign.
Internet mogul Kim Dotcom says he made two $25,000 contributions to the fund.
Mr Banks reported them as anonymous gifts, but Dotcom says he knew where the money had come from.
Labour leader David Shearer says New Zealanders expect politicians to respect the rules around transparency.
"It obviously has to be investigated. It will have to be, I think, a police investigation and I think if that's going to happen, and it should, then John Key will need to stand John Banks down in his role as minister until we've got clarity and the public have confidence."
Mr Shearer says there's no transparency, and he wants the donations looked into.
"We have very strict rules in New Zealand about election accountability and actually quite strict penalties where clearly if you break those, there's a two year possible jail sentence for example and you certainly have to stand down as a member of parliament."
Mr Shearer says New Zealand has a reputation as the least corrupt nation in the world, and he wants it to stay that way.
The question of whether he knew about Dotcom's donations was put to him several times on TVNZ's Q&A programme this morning, but Mr Banks had one answer:
"I signed my return honestly, I have nothing to hide and nothing to fear and it will come out in the wash."
Mr Banks says he's done nothing to breach the Electoral Act.
"I think you think I came up the river on a cabbage boat. I can tell you that when I signed my declaration for the mayoralty, I signed it in good faith, in the knowledge as a Justice of the Peace, as true and correct. I have nothing to fear and nothing to hide."
Auckland University political scientist Doctor Raymond Miller says it's a serious breach of the Electoral Act to list a donation as anonymous, if the beneficiary knows where it's come from.
"And to offer advice beforehand as to breaking the amount into two lots of 25, and to phone up afterwards, if Dotcom is right, to phone up afterwards and thank him for the money which has come into his account, suggests it was not an anonymous donation."
Photo: John Banks (NZ Herald)