Meridian Energy says the electricity market doesn't need the wholesale change the Labour and Green parties are pushing for.
The parties have a joint policy to introduce a single buyer of electricity if they form the next government after this year's election.
Meridian chief executive Mark Binns says if the proposed change goes ahead, New Zealand will have to live with the consequences for 20 or 30 years.
''There are other ways we think that you can look at retail competiveness and make a few relatively minor changes in the way the market operates. You don't have to throw the baby out with the bath water.''
Mr Binns told a parliamentary select committee on Thursday the proposal would mean less investment in renewal energy because the up-front costs are greater.
He would like Labour and the Greens to release more details of how the policy will work in practice.