Labour Party leader David Shearer says a television interview with Act's John Banks this morning only created more doubt about the discloser of anonymous donations in the Banks' mayoral campaign.
Mr Banks is alleged to have asked internet Tycoon Kim Dotcom to split a mayoral campaign donation into two parts of $25,000 so it could remain anonymous.
The allegations come after police were asked to investigate Mr Banks' listing of a $15,000 donation from SkyCity as anonymous.
Mr Banks denied any wrongdoing when he appeared on TVNZ's Q + A programme this morning and called the allegations a "sideshow".
"I can tell you when I signed my declaration for the mayoralty, I signed it in good faith in the knowledge it was true and correct. I have nothing to fear and nothing to hide and I welcome the inquiry," he said.
Mr Banks did not directly answer interviewer Paul Holmes' repeated questions about whether or not he knew Dotcom had donated the $50,000.
"I have nothing to hide and nothing to fear. It will all come out in the wash," he said.
Mr Shearer was not satisfied by this answer and reiterated his call for Mr Banks to resign as a minister.
"Alleged breaches to electoral law and the anonymity of political donations are serious, and yet John Banks seemed indignant to the need to answer even the most basic line of questioning on the donations he received from SkyCity and Kim Dotcom.
"They were simple questions. Fluffing answers about the number of donations he received is unnecessary and over-complicates the allegations.
"I think we can all agree that Kim Dotcom is a pretty memorable guy, and $50,000 is a cash injection even the most affluent campaigner would remember."
A spokeswoman for the prime minister said Mr Banks had assured him he had complied with local body electoral law.