Labour's Finance Spokesperson Grant Robertson says National's Finance Spokesperson Steven Joyce must apologise for his "patently false and cynical attack on Labour's Fiscal Plan".
Mr Joyce on Monday claimed Labour made an error in its costings, leaving a gaping $11.7b hole in its planned spending.
Mr Robertson says Mr Joyce's allegations have been "debunked" and he "has actively misled New Zealanders in a desperate and disingenuous hit job, and owes them an apology".
The call for an apology comes after numerous economists have publically said Labour's fiscals add up.
Mr Robertson says Mr Joyce is alone in his denial and "all credible economists say he's got it wrong".
Mr Robertson likened Mr Joyce's allegations to a conspiracy theory.
"I could put out a press release saying the Earth's flat, even though everyone else says it isn't, and just stand in a room saying it over and over again," he said.
Mr Robertson issued a fiscal hit of his own, saying National needs to explain how it would pay for its second families package, which National said it would roll out as part of its goal of lifting 100,000 children out of poverty, a commitment made by Bill English during Tuesday night's debate.
But National's not letting go of its $11.7b fiscal hole claims.
Mr Joyce said on Tuesday Labour is "maintaining the fiction" its operating allowances are correct.
If Labour's correctly budgeted, Mr Joyce says it "would be left with basically no allocation for increased spending in any area of government outside of health and education for two budgets."
"That's no new money for wage increases for police, social workers and DOC conservation rangers, for pay equity settlements, for the Ministry of Vulnerable Children, and no money for science and innovation, defence, or law and order."
Mr Joyce said that amounted to billions of dollars.
When questioned by media, Mr Joyce avoided saying whether he'd resign if he's wrong. "I've just asked them to add up their numbers," he said.
When asked if an independent economist could verify his claims, Mr Joyce mentioned the Taxpayers' Union, which is widely regarded as a right-wing lobby group.
The Taxpayer's Union told Newshub it believes there is a hole but it's not $11.7b and they are still working through it.