Labour's finance spokesperson has accused his National Party counterpart of spouting "fake news" and says he's "damaged democracy".
Grant Robertson said Steven Joyce's allegation of an $11.7b 'fiscal hole' in Labour's budget is "an absolute disgrace".
Mr Joyce continues to stand by the allegation, despite a swathe of economists and journalists saying it's not true.
- Economist consensus - there's no $11.7b hole in Labour's budget
- Steven Joyce standing by $11.7b 'fiscal hole' claim
During RNZ's finance debate on Thursday, Mr Joyce was asked by journalist Guyon Espiner to name one person who backs his allegation.
Mr Joyce said Bill English and the National party backed him, but couldn't name any economists.
"I'm not going to reveal people that I've had conversations with without asking them," he said.
"If you do their allowances the way that everybody else does their allowances you get an $11.7 billion hole.
"They're saying they'll run zero Budgets which is entirely unbelievable."
Mr Robertson took aim at Mr Joyce as the debate drew to a close.
"Steven made a very specific allegation this week which was a lie. Not one person in New Zealand has backed that up. Steven, this is a disgrace, you have damaged democracy by what you have done. This is fake news... you made an accusation which you know not to be true that no other person has backed up," he said.
"Do you know what New Zealanders have learned this week Guyon? They can't trust the Minister of Finance to tell the truth. It is a disgraceful situation Steven and you know it and you owe New Zealanders an apology."
Mr Joyce was given the final word in the debate and said, "Grant you're overreacting.
"The simple reality of it is you need to be able to cope with being questioned on your numbers, I made the questions because they're accurate and you've changed your figures."
Mr Robertson fired back: "We responded and you kept lying."