The organisation released packaged fudge from the 'Nicola Fudge Co.', branded with an image of Willis with the slogan, 'A treat today - A tax tomorrow'.
One union is describing the fudge and debate as a "shameless right wing stunt".
TPU chairperson Ruth Richardson said Prime Minister Christopher Luxon had condemned the previous government's 'sugar-rush economics', but that this government had "reached for the same lolly jar".
"Government spending has actually increased - both in real terms and as a proportion of the economy - since Grant Robertson left office," she said.
Speaking on RNZ's Morning Report programme today, Richardson called the situation "deadly serious" and said the country could not continue on its current debt track.
New Zealand needed to get in good financial shape or it would end up "with the worst of all worlds" - high inflation and low growth, she believed.
"Are we anywhere near a surplus? No. Is debt coming down? No. The level of public spending is not coming down and the number of public servants... has scarcely been touched.
"The books unfortunately are not in the shape that [Willis] would claim, it's no use shifting the goal posts and pretending when we look at surpluses that we shouldn't count certain expenditures, and it's no use continuing to say 'I'm saving money' but I'm just repurposing it and spending it elsewhere.
"We're all vulnerable if we are fuelling public spending in a way that's going to fuel inflation ... that's why we're running a campaign to say get a grip on the figures, get a grip on what's out of control, and ensure that we now have the kind of budgeting that we've not had under the previous Labour government."
Richardson said the TPU was being "very constructive" and said there were $35 billion worth of "proper sensible savings" to be made.
"Those are the paths to recovery."
Richardson initially laughed it off. But the Taxpayers' Union later issued a media release, saying she was "more than happy" to debate.
An opinion article from Newstalk ZB host Heather du Plessis-Allan claimed to have heard Willis' office "would prefer to do it next year".
In response, TPU spokesperson Jordan Williams said Richardson had picked next Thursday on ZB and Herald Now after Willis said she would debate Richardson "anytime, anywhere".
A spokesperson from Willis' office said she had not pulled out of anything and was just sorting out the details.
Yesterday, Willis said she was proud of her government's record of reprioritising spending.
"I really want the chance to defend our government."
Last year, debt as a percentage of gross domestic product remained level for the first time in six years. Spending as a percentage of GDP fell.
TPU head of communications Tory Relf told RNZ the organisation was all about "good policy" and did not mind which party it came from.
"We will work with whoever it is to deliver that good policy, and right now Minister Willis is not delivering it."
Relf said it was not about attacking Willis as a person.
"She is Minister of Finance, the same way they did 'Robbo's Removals' when he was Minister of Finance.
"Whoever was in that role, there would be a play on words or a gimmick to draw attention to the issue."
In response to the campaign, Willis told RNZ the government was putting the books back in order.
"I'm not going to comment on silly stunts. I want a debate on the substantive policy issues."
The TPU would not disclose how much the campaign cost, but said it had been done internally.
Shameless right wing stunt, says PSA
In a statement, the Public Service Association union today described the debate and the associated fudge as a "shameless right wing stunt".
National secretary Fleur Fitzsimons said the expensive boxes of fudge were a "deliberate false-flag operation to make Willis seem more moderate than she really is".
The Labour Party had earlier said the "public duel" was being used as a distraction from what really matters to New Zealanders.
"Nicola Willis is no moderate. It's her decisions that have seen $20 billion given away in tax cuts and handouts to landlords, big tobacco and businesses.
"It's her decisions that led to our health system being underfunded and under strain. It's her decisions that cancelled pay equity for over 150,000 women to prop up her Budget. It's her decisions that have seen thousands of public servants laid off, including over 600 scientists and researchers."
She said the "Taxpayers' (not-a-) Union" was "trying to shift the Overton Window - to make this prescription for austerity appear mainstream and normalised so it doesn't cost votes.
"New Zealanders won't be fooled by this gaslighting ... the PSA will not be eating the tainted fudge we received."
