National Party MP Claudette Hauiti has given up her parliamentary charge card after she used it to pay for a personal trip to Australia.
"I went to Australia. It was travel only and way outside Parliamentary Service guidelines," she told Fairfax Media.
She said the trip over Christmas last year and other questionable spending, including refreshments for a hui on a marae, had cost about $200, which she has since repaid.
"Of course it's absolutely no excuse for not knowing the Speaker's rulings. It is my responsibility and I didn't do it."
Parliamentary Service refused to provide a total of unauthorised spending, or comment on the matter.
"A new release of parliamentary information protocol has just been presented for debate in the House, and it would appear that this information is covered under it.
The Service cannot make any comment. Any requests for information should be made to the member," a spokeswoman said.
Ms Hauiti entered Parliament in May 2013, replacing disgraced list MP Aaron Gilmore.
Taxpayers' Union Executive Director Jordan Williams said workers have been sacked for similar offences.
"If an employee charged a trip to Australia on the staff card, they would be sacked. How can someone be trusted to run the country when they can't be trusted with the plastic?"
Earlier this year Ms Hauiti was caught out breaking Parliament's rules by employing her civil union spouse in her electorate office.
"This is not the first time that Claudette Hauiti has played fast and loose with taxpayer money. Although she replaced Aaron Gilmore, she should be setting a higher standard.
"Rather than cover-up MPs' actions, Parliamentary Services should let the public be the judge of how MPs are spending taxpayer money. We are calling on Parliamentary Services to disclose the full details of all MP misspending."