The Green Party won't be standing a candidate in the likely Mt Roskill by-election.
The current MP for Mt Roskill, Labour's Phil Goff, is running for the Auckland mayoralty and is a strong favourite.
If he does win in October, he will resign from Parliament, sparking a by-election in his electorate.
Green Party co-leader Metiria Turei said, after several weeks of internal discussions, the party had decided not to contest the probable by-election.
It is the first electorate deal done under the memorandum of understanding (MOU) that the Greens and the Labour Party signed this year.
Mrs Turei said, while Labour didn't ask the Greens not to stand a candidate, the two parties had been in discussions about the by-election under the MOU in recent weeks.
Mrs Turei said the Greens didn't want to give the National Party a better chance of winning the seat, in what could be a closely-fought by-election.
"We've looked at our priorities as a party, our priority is to change the government in 2017 - we certainly don't want to see National take a seat before the election," Mrs Turei said.
"We're a reasonable size party but we have limited resources and we're 12 months out from an election ... our party has decided, it has taken some time for that process to work through but we're announcing it now, as soon as we can, so the public is really clear about what we're doing."
Mrs Turei said the Greens had so far had several conversations with the Labour Party under the MOU.