Television New Zealand is investigating its Maori and Pacific Unit, because some of its staff members used company resources to carry out Labour Party business.
The unit's general manager, Shane Taurima, resigned on Monday.
Documents leaked to 3News show a TVNZ office was used for a Labour campaign meeting in August, and at least one staff member used the company email to conduct Labour Party business.
They also revealed Shane Taurima was involved in a Labour Party hui in January.
TVNZ says the actions are a serious breach of its editorial guidelines and expectations of independence.
The Labour Party says the matter relates to Taurima and TVNZ, and it is not appropriate for the party to comment.
Taurima had previously put himself forward to be a Labour Party candidate.
Head of news and current affairs at Television New Zealand, John Gillespie, says the issue reflects badly on its editorial independence.
"It's a cornerstone of what we do here every day, 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."
