Simon Bridges says "sly" Sir Michael Cullen is only billing for two days' work this month because he's been "caught out".
Sir Michael, the former chair of the Tax Working Group, is being paid just over $1000 a day to talk about its controversial recommendations - despite its final report being issued a few weeks ago.
"[Mr Bridges] is going out and - I'll try and be diplomatic - misconstruing what is in the report and putting a whole lot of inaccurate hypotheticals out there that I think need to be dealt with," Labour MP Kris Faafoi told The AM Show on Friday.
Mr Bridges says the Government has been paying Sir Michael, a former Labour Finance Minister, to do its "dirty work".
"I think, on Sir Michael Cullen, there has been a corrupting of the process," he told Newshub Nation on Saturday.
"We have someone now who has moved from being chair of a Tax Working Group to being a Labour Party politician who is doing the dirty work for [Prime Minister] Jacinda Ardern and [Finance Minister] Grant Robertson that they don't want to do. And what's more, he's doing it at $1000 a day."
Sir Michael defended himself during the week, telling RNZ's Morning Report he was only planning to bill the taxpayer for four days' work in February and March, and was pointing out errors on both sides - not just National.
"There've been a very large number of statements put in the public arena which are lacking in accuracy and often misrepresent what the report actually says and in some very important instances."
Mr Bridges said Sir Michael was probably going to ask for more money, but had to change his plans after criticism from the Opposition.
"It may well be that now he does rather fewer days than he was going to, given that he's been caught out in the game. But I think he's been rather sly. He said that National's hysterical. He's effectively inferred on Morning Report that I should not be believed. I call it as it is - that's political, and it's a corrupting of the process here, post the report."
He also suggested Sir Michael would keep talking publicly about the report regardless of whether he's getting paid or not.
"I got an email inviting me - he probably didn't want me there - to a Tax Working Group special run by KPMG and him in Tauranga, my home electorate. Is he doing those around the country? Is he on a roadshow? Maybe he's dialled that back.
"But you bet your bottom dollar when he signed up to that, he thought he was being paid $1000 a day to do the government's dirty work for it."
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When National convened its Tax Working Group in 2010, chair Bob Buckle wasn't paid a cent.
"I wasn't paid anything extra to do this. This was something I agreed to do," he told RNZ.
Mr Bridges infamously spent more than $100,000 in taxpayer money on travel and accommodation last year in just three months, touring the country in an effort to boost his visibility in the early days of his leadership.
Newshub.
