Fresh allegations have surfaced about donations to John Banks' Auckland mayoralty campaign as the ACT leader clung to office for another day.

Questions were raised yesterday about a $15,000 gift of "radio advertising" to his 2010 mayoralty campaign. Police are investigating other donations to his failed campaign.

Mr Banks admitted yesterday he got a discounted deal at internet mogul Kim Dotcom's favourite Hong Kong hotel, after initially denying he got cheap rates for the Christmas holiday.

Prime Minister John Key continued to back Mr Banks, but still has not talked to his embattled minister outside Cabinet.

Labour MP Trevor Mallard said it would be "absolutely weird" that $15,690 worth of radio advertisements could be donated anonymously, especially as they must be approved by a candidate, or his or her nominee.

"If it pretends to be anonymous and it's not, then that is a breach of a law."

Last night, Mr Banks, a former breakfast radio host, did not respond to a request for comment.

On Wednesday night he produced his Hong Kong Grand Hyatt bill and insisted Dotcom, who rented the top floor for six years, had not negotiated cheap rates.

Yesterday, Mr Banks said he arranged the reduced price of $678 a night himself. "I always negotiate prices down. I don't believe in paying the rack rate in a hotel."

He had earlier challenged Mr Mallard to repeat allegations outside Parliament that the internet tycoon had arranged the deal. Mr Mallard refused to back down.

Mr Banks has come under fire for not being upfront about his relationship with Dotcom, who says he was asked to split a $50,000 donation to Mr Banks' mayoral campaign. The Megaupload millionaire is fighting extradition to the United States on charges of internet piracy and money laundering.

Mr Key is rejecting opposition calls to stand down the small-business minister.

He said the furore about Mr Banks' discounted hotel room was a "far-fetched argument".

"He's assured me he paid for all of his own personal expenditure and if he's got a slightly better room rate ... well that's great."

He went on: "I'm not going to fire someone for complying with the law... there is no responsibility around ethical standards prior to them getting their [ministerial] warrant. Otherwise, everyone that would come to Parliament would have to have led a life of blameless excellence and, with the greatest respect to my parliamentary colleagues, most of them would fail that test."

Last night, National insiders rejected suggestions National was polling in Mr Banks' Epsom seat.

- © Fairfax NZ News