Just under a week before polling day and National is raising the prospect of a hung Parliament or a second election if National and ACT fall short of being able to govern alone.
NZ First's Winston Peters says the suggestion is an "unfortunate misunderstanding" that must surely be a mistake.
You can sense the pressure mounting as the campaign rolls on - days out from an election that is going to be tight. Luxon really, really does not want to work with New Zealand First - a fact he makes clear every day on the road.
Rhonda from Kerikeri asked him: "How are you going to cope with Winston?"
"Well, my preference is not to deal with New Zealand First," he told her, "and the answer, that's what I've been saying over the last few weeks, is if we don't want that uncertainty I think a government actually with two moving parts, meaning a two-party coalition, is a much better proposition, and that's why I'm saying to New Zealanders party vote National, give us a strong stable government."
But it is a possibility Luxon left wide open in the lead-up to the election campaign, and one he actively highlighted to supporters in a video just a few weeks ago, announcing he would work with them if he needed to. The polls suggest he will indeed need to.
NZ First late last week also released its policy manifesto for the election, laying out priorities including a tax-free income bracket under $14,000, a regional infrastructure fund, and an expensive promise to fund dementia and aged care beds - additional expenses in an already tight spending environment.
National's campaign chairperson Chris Bishop upped the ante on Sunday, telling the NZ Herald of a "very real and growing possibility" of a hung Parliament - either as a result of the three parties being unable to agree, or an even split of seats between the left and right.
"We are concerned there would be an inability to strike a deal in the interests of the country," Bishop said, "and that would necessitate, essentially, a second election.
"We will pick up the phone if we have to and try to make it work. But there is a real possibility of the necessity of a second election and it's a growing one, unless people cast a strong vote for change."
Peters was disparaging, saying NZ First had "come to the conclusion that Chris Bishop has made these comments by mistake".
"These very concerning comments must be an unfortunate misunderstanding because suggesting the National Party would start scaremongering and threatening to ignore the will of the people on Election Day and ignore the need of our country to form a stable government would be highly troubling to voters.
"It is telling voters National would instead enforce another costly election on the nation purely because of their own political expediency.
"We will be back in numbers that will surprise Mr Bishop - and it's clear to us now he knows that. Mr Bishop don't panic, help is on its way."
ACT leader David Seymour said New Zealand could not afford a second election, and it was the last thing people would want to see. He pledged to do everything possible to avoid going to the polls again, including trying to put together a government with New Zealand First.
"If you look at Winston Peters' past performance in government, it is destabilising. We will make our best effort to make it work."
Following Luxon's conversation with Rhonda, reporters asked how likely he though it was an agreement could be reached between the three parties.
"What I have said is that I would pick up the telephone, talk to Winston Peters and New Zealand First knowing that they haven't come with us for 27 years, remembering 2017, and that's why I say to New Zealanders you have six days to, actually if you want change, you have to step up to the plate and vote for it," he said.
He moved to defend Bishop, however, when asked if his comments were scaremongering as Peters claimed.
"Well, no, that could be one of the complexities that emerges and one of the uncertainties that emerges on the other side of an election."
He did not regret ruling out Peters earlier in the campaign, he said, but questioned over whether he had looked into the policies of this potential coalition partner, he said he was "aware of some of them".
"As a last resort, and in order to avoid three years of chaos from this government and more of this malarkey carrying on, I will pick up that phone."
Labour leader Chris Hipkins came back to the campaign after a week in isolation, seemingly with renewed vigour, and in-fighting among his opponents will be music to his ears.
He made clear to reporters his position on working with NZ First had not changed.
"After spending the last few weeks telling New Zealanders that he could work with Winston Peters, Christopher Luxon is now threatening New Zealanders with another general election," he said.
"I made it clear months ago we wouldn't be working with Winston Peters and New Zealand First ... I want people to give their party vote to Labour so that we don't have to have another general election."
He confirmed he would maintain his position even if it meant sending New Zealand back to the polls.
"Labour will not work with Winston Peters and New Zealand First, we do not believe that's a recipe for stable government."