Opposition parties have warned the partial sale of three state-owned power companies will put the security of the country's electricity supply at risk.
The Government intends to sell up to 49% of Genesis Energy, Meridian Energy and Mighty River Power as part of its partial asset sale plan.
A letter from Genesis Energy to State-owned Enterprises Minister Tony Ryall, obtained by Radio New Zealand under the Official Information Act, confirms the generator is closing down Unit One at Huntly Power Station by the end of this year.
The Labour and Green parties say the move is about making it a more attractive proposition for sale.
Green Party co-leader Russel Norman says Genesis is proceeding with its plan despite its likely impact on the security of supply.
But Energy Minister Phil Heatley says he's confident the electricity market will ensure there's enough capacity to keep the system running.