The auditor-general wants the legal clout to require MPs to answer questions and provide documents when she is doing an inquiry.
A parliamentary committee is reviewing the rules for pecuniary interests and considering recommendations to improve disclosure, for example, MPs having to reveal all trusts they have an interest in and give information about share trading.
Controller and auditor-general Lyn Provost and her deputy Phillipa Smith were today asked about their role investigating complaints when MPs failed to declare interests.
Ms Provost said she had no strong views about which department did inquiries but if it was hers, she wanted beefed up powers.
"The Standing Orders (Parliament's rules) say we can inquire but we asked for the same powers in the Public Audit Act and that didn't go through."
She asked for an amendment to require people to give evidence and provide documents.
Labour MP Trevor Mallard said the inquiry report into an MP would be made public and that would show if an MP had refused to cooperate.
"I can't imagine anyone who wanted to continue being a member of parliament not supplying you with what you requested."
ACT leader Rodney Hide said the Winston Peters case highlighted serious instances where information was not declared.
In 2008, Mr Hide laid a complaint that went to the privileges committee, which acts as Parliament's court, over New Zealand First leader Mr Peters failing to declare a $100,000 donation from expat businessman Owen Glenn toward his legal fees.
At the time Mr Peters was foreign minister and he had pushed for Mr Glenn to be appointed honorary consul in Monaco. At first Mr Peters denied the donation had been made, then once it became public denied that he had known about it.
The committee found on the balance of evidence Mr Peters had known about the donation and he was censured for not disclosing it. Various authorities investigated Mr Peters but no charges were laid.
Ms Provost said if the case was forwarded to her she would have investigated.
"Our issue becomes if that members says 'I will not give you information'."
During a recent inquiry into housing allowances MPs had to answer questions because public money was involved but when it came to other funds they did not have to.
The Auditor-General has no power to ask third parties for information either, for example lawyers in charge of NZ First's trust, or Mr Glenn.
Speaker Lockwood Smith asked if the auditor-general wanted those powers.
Ms Smith said that wasn't what the department was after.
"That would be an extension beyond the powers we have in other areas... I think we'd think very seriously before asking for such powers, because it would immediately conflict with the rights of people."