A study commissioned by Business New Zealand concedes that the Labour and Green Parties' policy of having a single buyer of electricity would lower power costs to consumers.
But it argues that the benefits would not be big enough to justify introducing the policy.
Business New Zealand says the latest study by economics consultancy Infometrics has found households will only be $120-a-year better off under the policy, not $300 as claimed by the opposition parties.
The study also argues that lower power prices will simply encourage greater use of electricity.
Greens' energy spokesperson Gareth Hughes says the business lobby group has finally admitted the plan will be good for the economy but it needs to stop down playing the benefits of the policy.