Environment Minister Marian Hobbs says "the decision's been made" on the inquiry into genetic engineering - and she will not add any extra commissioners.
National's Gavan Herlihy claims the current four person team is unbalanced - as none of them have an agricultural background.
Mr Herlihy's calling for a fifth commissioner to be appointed, to ensure the team's results are unbiased.
But Ms Hobbs says the commissioners will have a skilled team of support staff to help with their inquiries.
She's confident interested parties, including farmers, will bring all necessary information in front of the commission.
