John Key is dismissing Green Party criticism that his chief of staff attending a National Party fundraiser meant he was there as Prime Minister, not as an MP or party member, which breaches his own rules.
The Greens say it is another example of the wealthy having access to government in return for boosting National Party coffers, which must raise questions about a conflict of interest.
Green Party co-leader Russel Norman said the Wellington dinner in September 2011 charged $3000 a head and since Mr Key was there with his top staffer, Wayne Eagleson, he was there as prime minister.
Dr Norman said that was a breach of Mr Key's own directive to government ministers that they attend so-called Cabinet Club events only in their capacity as MPs or party members.
He described it as fundamentally corrosive to democracy.
But a written statement to Radio New Zealand News said Mr Key attended the dinner as leader of the National Party.
"Mr Eagleson is responsible to Mr Key in both his capacity as Prime Minister and as Leader of the National Party.
"In the time National has been in Government Mr Eagleson has attended a handful of National Party fundraising events."
A spokesperson from his office earlier said the Greens' attacks on National Party fundraising highlighted their push for political parties to be state-funded because the Green Party has trouble raising funds.
Dr Norman said Mr Eagleson was employed by the taxpayer and ministerial services to be the Prime Minister's chief of staff .
"So there's no defence any more that the Prime Minister was simply there as an MP or as a National Party leader. He was there as the Prime Minister with his prime ministerial support staff with him."
Dr Norman said serious questions over a possible conflict of interest had to be raised when people paid for access to the prime minister and the National Party benefited financially from that.
John Key's office said such a fundraiser was completely within the law.