TVNZ is reviewing all the work Shane Taurima has been involved in for about the past year as allegations of political bias are fired at him by National Party ministers.
Mr Taurima resigned yesterday after confirming to his bosses that he hoped to seek Labour's candidacy for the Tamaki Makaurau electorate.
Leaked documents given to 3 News showed he had taken part in a Labour Party Tamaki Makaurau electorate meeting on how to win the Maori vote.
They also showed TVNZ staff who had hosted a Labour Party meeting in TVNZ's offices last August, although Mr Taurima has denied knowing about the meeting.
Mr Taurima has denied showing bias in his editorial work for TVNZ, which included a stint hosting current affairs show Q+A.
He resigned from his role as head of TVNZ's Maori and Pacific unit, which gave him oversight of shows including Waka Huia, Te Karere and Marae Investigates.
Prime Minister John Key said the incident risked giving a perception of bias at TVNZ, "which I do not believe is there''.
He said when he had been interviewed by Mr Taurima, the interviews were "robust.''
"But the truth is I have a lot of robust interviews and I don't have a beef against him.''
However, other ministers believed Mr Taurima had treated them differently to Labour MPs.
Justice Minister Judith Collins and Social Development Minister Paula Bennett accused Mr Taurima of treating National Party women ministers particularly harshly.
Ms Bennett said she had informally raised with TVNZ an interview Mr Taurima did with her on youth unemployment and decided she would not appear on the show with him again. She said she did not know about Mr Taurima's wider work.
"I always felt he was much tougher on National Party Maori women. But you have to be careful you don't overthink these things.''
She said she believed it should have been obvious to TVNZ that Mr Taurima would have considered standing for Labour again after he sought the Ikaroa Rawhiti selection.
Education Minister Hekia Parata said she had been interviewed by Mr Taurima, but stopped short of saying she was treated unfairly saying while it was vigorous she felt she was "appropriately tested.''
Labour leader David Cunliffe said he did not believe Mr Taurima had shown bias in his broadcasting career, but it was important journalism was free from any perception of interference.
"I do think it's important for all channels that they are beyond any suggestion of political bias or interference.''
He said TV3 host Paul Henry had been open in a recent interview with Mr Cunliffe that he was not a Labour Party supporter.
"All politicians at this level know in any given day people are going to say things about them that they think are a bit unfair and occasionally untrue. That's part of the territory.''
He said he had done interviews he believed were unfair. "Pretty often one's perception in an interview might not be the same as the interviewers. That's part of the routine.''
Act MP John Banks said the revelations about Mr Taurima demonstrated why TVNZ needed to be privatised.
"This issue is not Mr Taurima's politics. It is the fact that he and some of his staff wrongly used taxpayer's property to further his political objectives''
"The easiest fix is for the taxpayer to get out of the television business. TVNZ should be sold.''
Kris Faafoi, Labour MP and former TVNZ reporter, said it was Mr Taurima's responsibility rather than Labour's to manage any conflict his political ambitions had with his job at the state broadcaster.
"He should have managed that himself. Shane has the ability as a private citizen to have political leanings but when it comes to his job he shouldn't take that through the door. He's taken responsibility for that.''
He said Mr Taurima was a professional in his role as a broadcaster, but had shown "bad judgement'' after deciding to seek Labour's nomination again.
TVNZ was investigating whether Mr Taurima had influenced the editorial content of the programmes he oversaw.
"When it comes to the state broadcaster, it has to be right down the middle. As a former staffer, I take the editorial independence of TVNZ very seriously, then and now.''
He said it was over to TVNZ to answer why they had put Mr Taurima back into his role as head of Maori and Pacific programmes after he stood down for his unsuccessful bid to be Labour's candidate in Ikaroa-Rawhiti.
Mr Faafoi was a reporter in TVNZ's Press Gallery office but left to work as former leader Phil Goff's press secretary in 2009 before standing for Labour in the Mana byelection in 2010.
Broadcasting Minister Craig Foss said he had sought assurances from the board of TVNZ that they were adhering to the Broadcasting Act and had been assured of that. He said TVNZ was investigating the matter now.
Earlier, Taurima "categorically denied'' his political affiliations influenced editorial decisions following the revelations.
Read Shane Taurima's media statement here.
In statement this morning he said he fully accepted that some of his actions in supporting the Labour Party crossed a line.
Mr Taurima said he had been a member of the Labour Party since contesting the Ikaroa-Rawhiti candidacy in 2013.
"I have attended party hui and fully accept that some of my actions in supporting Labour may be seen to have crossed the line and I apologise unreservedly.
"I categorically deny that my political affiliations have had any influence on any editorial decision that I have made during this time or at any time in the more than 12 years that I have been honoured to work in many roles at TVNZ.
"However, questions have been raised that have brought into question the integrity of the crucial work of my colleagues at TVNZ. This is unfair and unacceptable and as a result I have resigned.''
He denied that other staff members in his former unit were political activists.
- Cunliffe 'not aware' meeting held at TVNZ -
Labour leader David Cunliffe told RNZ this morning he was not aware until yesterday that a Labour Party meeting had been held at a TVNZ office.
"Mr Taurima is no doubt a very good person but he has shown a lapse of judgement in that regard and that is now a matter for him and his former employer.''
Media should be "neutral and unbiased and free from political influence and involvement'', Mr Cunliffe said.
He said he had never attended a political meeting at a TVNZ building.
- TVNZ head of news: It reflects badly on us -
TVNZ head of news John Gillespie said the events reflected badly on the whole of TVNZ.
"I have to say that we are gutted by that...we take our editorial independence incredibly seriously - it's a cornerstone of what we do here everyday, it always will be a cornerstone of what we do here every day.
"These people have nailed their political colours to a TVNZ mast. It is untenable.''
He said an investigation would look into whether there were any other anomalies.
"This goes to the heart of our editorial values and independence and it's something that we just can't abide by.''
Mr Taurima had been upfront that he was considering standing for Labour in Tamaki Makaurau at the next election and had briefed his bosses last week, Mr Gillespie said.
However, TVNZ had not known of Mr Taurima's involvement in the January hui or about the use of TVNZ offices to hold a Labour Party meeting, he said.