Labour leader Jacinda Ardern says her party will put in a regional fuel tax to help pay for Auckland's transport.

That is a "tough call" that will be unpopular but is necessary, Ardern told TVNZ's Q&A today.

Ardern, who spoke of growing up in Morrinsville and how "middle" New Zealanders were struggling, said making Aucklanders pay more for their petrol was only fair.

"This is a message to the rest of New Zealand as well - Aucklanders know that we have to contribute to the problem that we have, whilst building a partnership with central government to fix these problems."

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Ardern will unveil her plan at 1pm in Auckland's Wynyard Quarter - the proposed city terminus for a light rail link down Dominion Rd to the airport.

Ardern was also asked about working with New Zealand First leader Winston Peters - and suggested questions about whether she could do so effectively were because of her gender.

"I do find it interesting though as to why the question is being asked, 'could I work with Winston?' I don't hear that question as often asked of other political leaders."

Host Jessica Mutch asked if she meant the questions were being asked because Ardern is a woman.

"I don't want to waste too much time thinking about that," Ardern said. "I don't know, it could be a whole manner of things."

On Friday Ardern ruled out any chance of Peters serving a stint as Prime Minister under a Labour Government.

She also brought another potential coalition partner into line - revealing she told her team to advise Green Party co-leader Metiria Turei that she could not include her in a Cabinet role.

That came after further revelations about Turei's time on welfare in the 1990s, and the admission she had enrolled at her ex-boyfriend's flat so she could vote for a friend of hers. Although Ardern denied she had forced Turei's hand, in effect that left Turei with little choice.

On Friday afternoon, Turei held a press conference to say she would not be seeking a ministerial role.

Asked on Q&A why she chose to reveal she had blocked Turei from a future Cabinet position, Ardern said she was being transparent.

"I was asked. I was asked. And it was important that I give an honest reflection of what I would do in that scenario.

"It shows that I work with integrity. And I would also be very open and transparent with the support partners I work with, as much as with the public, when asked.

"I didn't sit there and reflect on what this demonstrated. I just did the right thing."

Green Party co-leader James Shaw also appeared on Q+A and said Turei had already made up her mind to rule herself out of a Cabinet position, before Ardern's staff contacted the Green Party on Friday morning to say Turei would not be in Cabinet in a Labour Government.

Shaw, who said he talked to Ardern this morning and passed on his congratulations, said the phone call from Labour did not influence Turei's decision.

"She had decided. And what we did was we said, well, what would we normally say to, for example, a minister who was attracting this kind of level of criticism. And normally we would ask them to stand down for a period of time. So this was the equivalent of how we would treat any other politician in Parliament."

Ardern was also asked a series of quick fire questions on policy, and said she would not campaign on a capital gains tax, or raising the retirement age.

Labour's Auckland issues spokesman Phil Twyford said Labour's transport plans had been influenced by the Greater Auckland lobby group, which proposes a "congestion-free network" including light rail from the airport, up what is now the Northern Busway to Orewa and along the northwestern motorway.

Twyford said Ardern would also reveal today how Labour would close a funding gap of at least $4 billion for the first decade of the agreed plan.

"Auckland is a third of the country by population, so it's fair that the Government contribute its share towards the National Land Transport Fund, but we have to find ways of making Auckland's growth self-funding," he said.

"That's why we will be announcing various ways in which Aucklanders will contribute to the cost."