The Prime Minister thinks National should "go back to the drawing board" after the centre-right party announced a policy of delivering "taxpayer receipts" to every taxpayer outlining their tax paid and where that money has gone.
"If the thing that the National Party think is the most pressing priority for New Zealanders is to receive effectively a bank statement of how much they've paid in tax I think suggests that they've got their priorities all wrong," Chris Hipkins said.
The ACT Party says it's not even an original idea. In fact, David Seymour says ACT proposed the policy 25 years ago and it was National that vetoed it.
"We can only hope it doesn't take a quarter of a century for our colleagues to adopt all of our ideas," Seymour said.
National leader Christopher Luxon announced the idea on Monday as one of three ideas to "boost fiscal discipline" and improve transparency about where Kiwis' money is going.
"Every taxpayer will receive a 'Taxpayer's Receipt' from Inland Revenue, showing taxes paid and government payments received including Working for Families and benefit payments," National revealed. "It will break down where taxpayers' money has been spent, eg education, health, and welfare."
But questioned by media after the announcement, Luxon couldn't say how much the idea would cost. He said it was "very achievable" and "straightforward", however.
"We could fund it well within baselines," Luxon said.
"What we are talking about is a change of behaviour and a change of practice, something we used to do in Government for many, many years and decades this way. We need to make sure we've got good cost evaluation upfront."
Luxon said Kiwis should have "more literacy about where government spending goes and where their taxes go". He expects it would come out with Kiwis' annual tax returns.
Asked if it was hypocritical to blast the Government's spending and then unveil an uncosted policy, Luxon said: "I'm giving you a sense of how we are going to manage in Government".
"What I'm being really clear about is I expect when we spend taxpayers' money, we know whether we got a result or not. I expect New Zealanders to understand where that money is gone. And I also expect our CEOs and their top teams to be very focused on delivering outcomes for New Zealand."
And how many staff will Inland Revenue need to administer the receipts?
"With 14,000 more public servants in Wellington since this Government came to power, there is plenty of resource to do it."
National would also require Treasury to report annually on the performance of major programmes "to demonstrate whether they are achieving results" and also link public sector chief executives and deputies to achievement "in order to encourage high performance and ensure accountability".
"The reality is it's a core function of Treasury, is to make sure that there are strong business cases before initiatives are launched and importantly, to make sure they are a really strong evaluation afterwards," Luxon said.
But the taxpayer receipt idea has been all but dismissed by the Prime Minister, who appeared initially speechless when asked about it.
It would be an "incredible waste of money", he said.
"I mean, ultimately, anyone can look up on the MyIR website any day, how much tax they have paid. That information is publicly available every year when the Budget is released, we release a summary of where taxpayer money goes, what New Zealanders are buying for their taxes.
"I mean, effectively, I think the National Party now seem to be proposing to send out 4.3 million spin doctor-type letters to people explaining where their tax dollars are going."
He said National's "priorities are in the wrong place", especially in Budget week.
"This is their opportunity to set out what they would do differently in Government, if this is the best they can come up with, I think maybe it's time for them to go back to the drawing board."
Hipkins said someone would have to pay for those letters to be written and sent out.
"Ultimately, that's going to involve employing people to do that."
The ACT Party said New Zealanders don't need Treasury bureaucrats to tell them their money is being wasted - and said its alternative Budget released on Monday laid out wasted expenditure.
"We don't need bureaucrats or consultants to tell us there's wasteful spending happening. We know it is. Let's get on with it scrapping it," Seymour said.
"New Zealand cannot afford another cycle of retaining left-wing policies so Labour and the Greens can pick up where they left off. What is needed is real, clear-sighted and specific change in Government.
"Issuing taxpayers a receipt for what they pay is a good idea, too. It is also an idea with an interesting history. Twenty-five years ago, ACT proposed this exact policy, but the-then National Finance Minister used a financial veto to stop it."
Luxon said he wanted to "restore fiscal discipline".
"I won't put up with pouring more money into broken programmes that don't work when we need more funding for frontline services like schools and hospitals," Luxon said.
He believes the idea of a taxpayer's receipt would explain government spending to the public, therefore improving accountability.
"It's taxpayers' money and we all deserve to know what it's being spent on but unless you've worked in the machine in Wellington, or have trained for years in accounting or economics, it's impossible to work out how much money the Government spends, and where it all goes.
"That's why a Government I lead will introduce new requirements for clear financial reporting to taxpayers. Individuals will receive a taxpayer's receipt each year and Treasury will produce an annual Report Card for Taxpayers to clearly show government spending and tax."
This comes ahead of the release of the Budget on Thursday.
