Decision to keep him in his job had been a mistake in hindsight, says chief executive.
TVNZ chief executive Kevin Kenrick says the state broadcaster gave Shane Taurima a journalism or politics ultimatum when he was reinstated at TVNZ after his venture into politics last year and revelations of the extent of his involvement with Labour since then were "very disappointing".
A review team is now set to probe the extent of Mr Taurima's involvement with the Labour Party while he was working at TVNZ, involvement by other staff and any impact it had on the broadcaster's editorial work.
Mr Kenrick said TVNZ had sought commitments from Mr Taurima after his tilt for Labour at the Ikaroa-Rawhiti candidacy before restoring him to his role heading the department. "The key focus was to get him to make an explicit choice between journalism and politics, and to make commitments around that. We relied in good faith on those commitments."
Mr Taurima's solid 12-year record at TVNZ had been a factor in the decision to reinstate him.
He said this week's revelations had been very disappointing and the decision to keep Mr Taurima in his job had been a mistake in hindsight.
Mr Kenrick said Mr Taurima told them last week he had been approached to stand for Labour again and was considering it.
"We reaffirmed it was either journalism or politics and you need to make a decision promptly."
Mr Taurima had still not decided when he met news boss John Gillespie again on Monday, but resigned after leaked documents to 3News showed the use of a TVNZ office and staff involvement in Labour meetings. A TVNZ office was used to host a Labour Party meeting, and three TVNZ staff had used staff email addresses to help organise another meeting in Pt Chevalier last month which Mr Taurima was at.
It is understood Mr Taurima has now confirmed to TVNZ he was also at the meeting that took place at TVNZ after initially being unable to recall it. Mr Kenrick said the use of TVNZ resources for party politics was a breach of editorial guidelines.
Mr Taurima declined to comment yesterday.
Mr Kenrick said it was too early to say if other TVNZ staffers would face disciplinary action.
He expected the review to take at least two weeks and would involve an external expert.
There were checks and balances on editorial programmes before they were aired, and Te Karere had been under the joint management of news boss Mr Gillespie and Mr Taurima since the middle of last year.