Labour list MP Moana Mackey is using taxpayer money to rent her Gisborne electorate office from her mother.
Politicians must declare any pecuniary interests but the arrangement is within the rules for MPs, who are given a capped allowance to cover the cost of running offices outside Wellington.
Ms Mackey, recently promoted by Labour leader David Cunliffe, has an office in Customhouse St in Gisborne which property records show belongs to her mother Janet Mackey.
The pair were the first mother and daughter pair together in Parliament when Moana Mackey was elected through the Labour list in 2003 and Janet Mackey was the Labour MP for the East Coast electorate, until retiring in 2005.
Janet Mackey purchased the heritage building in April 2009 for $200,000 where Ms Mackey and the late Parekura Horomia, the Labour MP for Ikaroa-Rawhiti, shared their offices.
Ms Mackey - the Labour spokeswoman for science, the environment and climate change - could not remember the monthly rent bill but said it was below the market valuation.
"We had been there long before my mum bought it, possibly as long as Parekura had been in Parliament.
"We checked it all beforehand and made sure we complied with all the rules."
Ms Mackey said she now shared the ground floor of the building with Meka Whaitiri, who won the Ikaroa-Rawhiti by-election for Labour after Mr Horomia's death earlier this year, but taxpayers were not paying rent for each of them.
The Parliamentary Service does not comment or supply information about rents paid for electorate offices but does require a market rental evaluation "where the member has a direct or indirect interest in the property, or a relationship with the landlord".
Another Labour list MP, Louisa Wall, rents her Manurewa office from a company of which her partner is the sole shareholder and director.
The wider Labour Party owns five electorate offices which are rented back to MPs at the taxpayers' expense, while at least five National MPs, including Prime Minister
John Key, own their electorate offices which are rented to themselves.
Former State Services Commissioner Mark Prebble criticised MPs for buying their electorate offices and renting them back to Parliament in his book With Respect.