Opposition parties have been quick to react to the Cabinet resignation of Judith Collins, saying her implication in 'Dirty Politics' needs to be fully investigated.
New information from an email conversation in 2011 suggests Ms Collins may have undermined a director of the Serious Fraud Office, an allegation the former Minister denies.
Labour leader David Cunliffe says the revelations today are a "very, very serious development" and he is calling for a full commission of inquiry into the action of ministers and their offices.
"From what we so far understand it appears that the minister may well have been undermining a chief executive who was directly under her control - that would be completely inappropriate...to have a Minister of Justice seeking to gun for a chief executive who is in a very sensitive regulatory role has no place in New Zealand politics," Mr Cunliffe said.
Mana Party leader Hone Harawira says it is "just and appropriate" that Ms Collins has resigned from her Cabinet position following "scandal after scandal" over her relationship with Whale Oil blogger Cameron Slater.
"The evil to which they have descended and the way in which they communicated with one another about ordinary New Zealanders led to this decision," Mr Harawira says.
John Key and Judith Collins have been "working as a team in dirty politics for a very long time", Internet Party leader Laila Harre says.
"The convenience of the decision today does not change the fact that there needs to be a full investigation into the operations of the whole Government with more and more suggestions of corrupt activity," says Ms Harre.
The Greens say National's election campaign has been thrown into chaos with the "sacking" of Judith Collins over dirty politics allegations.
Co-leader Metiria Turei says National is totally immersed in dirty politics and Mr Key condoned it.
"John Key should have sacked Judith Collins the minute the extent of her involvement in dirty politics was revealed. Instead he sat on his hands until public pressure forced him to act," Ms Turei said.
New Zealand First leader Winston Peters says he feels exonerated by the events of today after earlier being called a liar.
"It's not to do with this email today, it's because of the other events. I think it's the end of the road (for Ms Collins)," Mr Peters said.