The Auditor-General has been asked to investigate whether the Finance Minister should be able to claim Wellington as his primary place of residence and collect an out-of-town allowance.
Bill English has been under fire since it was revealed he received a ministerial housing allowance of $700 a week for a Wellington property owned by his family trust.
He has since repaid $14,000 of the allowance, but the Opposition will not let the matter rest.
Labour has tabled a document in Parliament saying ministers must disclose any conflict of interest, including one relating to their families, when claiming allowances.
The Speaker has ruled that Dipton, in Southland, is Mr English's place of residence. However, Progressive Party leader Jim Anderton says he has decided to write to the Auditor-General for clarity on the ruling.
He says it is common sense that the minister lives mainly in Wellington and is therefore ineligible to claim a housing allowance.
Mr Anderton told Morning Report he wants to ensure the rules are applied consistently, as Labour's Marian Hobbs and Phillida Bunkle stood down as ministers in similar circumstances.
The Office of the Auditor-General says it will consider the request.
Mr English said through a spokesman that Mr Anderton's claim is "ridiculous".