Building and Construction Minister Maurice Williamson says he will deal with any conflicts of interest that arise from his role as a director of a company.
The company is Holyoake Industries Ltd, which provides air conditioning products to the building industry.
Mr Williamson has declared his directorship on the MPs' register of pecuniary interests.
On becoming minister, he says he instructed officials that he would not receive papers and would withdraw from discussions about heating and ventilation due to his position with Holyoake Industries.
Prime Minister John Key approved his directorship and continues to support Maurice Williamson. But the Labour Party says Mr Williamson should choose between his two roles, and either stand down as director or minister.
Noel Holyoake says his company has from time to time supplied collapsed company Mainzeal or sub-contractors working for it.
However, Mr Holyoake says it is not a creditor and has no relationship with Mainzeal. He is amazed that Labour has raised the matter.
Mr Holyoake says Mr Williamson has been a director for about 10 years and has helped immeasurably in the firm's computer operations.