Labour leader David Cunliffe says all ministers should be subject to a full commission of inquiry to get to the bottom of the allegations made in Nicky Hager's book Dirty Politics.
Mr Cunliffe has appeared on TV3's The Nation this morning and said a full commission of inquiry is needed into the allegations of dirty politics between Ministers in Parliament and Cameron Slater's blog Whale Oil.
"This is not what New Zealand expects of their government," he said.
Mr Cunliffe said former Justice Minister Judith Collins should have been gone "months ago."
Read more of our coverage:
• I'm the victim of a smear campaign: Judith Collins resigns
• Resignation reaction: 'Too little, too late'
• The email that brought down Judith Collins
• Collins resigns: Blogger backs mate
• Collins resigns: Jared Savage and Fran O'Sullivan respond
"What other Ministers have been involved in feeding information to that blog?
"It's got to be cleared up."
Resignation has not derailed campaign - Bill English
Meanwhile, Appearing on TVNZ's Q & A this morning, Deputy Prime Minister and Finance Minister Bill English said the allegations against Ms Collins were serious and "that's why the Prime Minister's launched an inquiry into them".
Suggestions that former Hanover boss Mark Hotchin was behind the smear campaign against ex-Serious Fraud Office (SFO) chief executive Adam Feeley were "all a bit bizarre", Mr English said.
"If that is linked through the email to any kind of ministerial conduct as is implied that's a serious issue, but we've yet to see if an email written by the blogger is correct or not and an inquiry will deal with that.
"Whatever the campaign might have set out to achieve, we have a high level of confidence in the Serious Fraud Office and the Financial Markets Authority."
Ms Collins' resignation had not derailed the National party's election campaign and Prime Minister John Key was right in waiting until yesterday to act, he said.
"The Prime Minister - as he said yesterday - made judgements on the facts that are before him. He's got a new set of facts today.
"I think he's made the right decisions and now there's going to be an inquiry into what is a serious allegation.
"It hasn't become bigger than the campaign. In the end the campaign's about the voters, this is an argument about a blogger, maybe a minister and a bunch of other people who generally aren't in the public eye."
Labour's finance spokesman David Parker, also appearing on Q&A described the revelations levelled in Nicky Hager's book Dirty Politics as "just the tip of the iceberg".
"This is absolutely unprecedented in New Zealand, the Minister of Justice [is] asserted to be undermining one of the arms of justice - this is very serious."
Email leaked from within National
New Zealand First leader Winston Peters said he believed the leaked email came from within National.
"What's happened here is someone's said 'she's got to go'."
He said he believed Ms Collins didn't stand down willingly.
"She didn't stand down, she was pushed but she jumped before that happened."
He said he had never seen a campaign so derailed from talking about policy and key issues.
Greens Party co-leader Metiria Turei said it appeared the leaked email that ended Judith Collins' career as a Minister could have come from within the National Party.
"I think [John Key] is responding to the public. He is campaigning, he's not acting like a Prime Minister."
She has called for a Royal Commission to investigate the allegations in Hager's book.
She said the Royal Commission needs to begin now, so evidence in Judith Collins' and John Key's offices could be preserved.
"We'll only get a Royal Commission with a change of government," she said
Mr Peters said he had called for a Royal Commission in to the allegations in Dirty Politics.