Deputy Prime Minister Bill English's claim his primary residence is in the Southland town of Dipton rather than the Wellington suburb of in Karori is coming under increasing scrutiny.
The watchdog on public spending is now looking into it.
The Office of the Auditor-General says it will make "preliminary inquiries"
into whether Mr English was right to claim the taxpayer-funded accommodation allowance for being an out-of-town MP.
Mr English's wife is a GP in Wellington and his children go to school there, but the city is officially his secondary residence.
His primary residence is Dipton, in the Clutha-Southland electorate he represents as an MP.
This arrangement has allowed him to claim $24,000 a year as a backbencher and now a $30,000 lump sum as a minister.
A spokeswoman for the Auditor-General said the office would gather "background information" to decide whether a full inquiry was warranted.
It is acting on a complaint from Progressive MP Jim Anderton, who wants to know whether Wellington is Mr English's primary residence.
The spokeswoman said: "We have not yet decided whether to inquire into this matter, but see it as appropriate for this office to make some preliminary inquiries to gather background information.
"Once we have had an opportunity to consider that information we will decide whether any further action by this office, such as beginning a formal inquiry, is warranted."
Mr English declined to comment.
Deputy Auditor-General Philippa Smith's letter to Mr Anderton said the Auditor-General would gather background information on how MPs and ministers were paid accommodation benefits.
A decision on whether a formal inquiry was needed would be given priority as there was a "measure of public interest in this issue".
This is expected to be made in a fortnight.
