Unison has become the first lines company in New Zealand to increase line charges for households generating their own electricity.
It announced last week higher fees for customers who use a combination of solar energy and the electricity grid in Hawke's Bay, Taupo and Rotorua.
The move attracted criticism particularly from the Labour and Green parties.
Sustainable Energy Association chairman Brendan Winitana said Unison's charge was "a clear abuse of monopoly power against ordinary Kiwis who are trying to reduce power bills and help stop climate change".
While Greenpeace executive director Russel Norman said just months after the world agreed in Paris to reduce emissions to stop climate change, a New Zealand company was specifically taxing solar energy users. Mr Norman said it was "extraordinary - and wrong".
Napier MP Stuart Nash said it was a backwards approach that set a bad precedent.
"Unison should be working with customers who go solar, rather than against them," Mr Nash said.
The lines company said solar electricity users connected to its network had been subsidised by other power consumers so a lift in charges was needed.
Home electricity generators paid about $300 less than other customers but received the same level of service.
Unison manager of business assurance Nathan Strong said this was not fair.
"We understand that solar consumers would like to receive a larger subsidy from Unison, but we don't think it's fair that other customers, some of whom are struggling families, should have to pay higher lines charges to subsidise their use of the network."
Mr Strong said the company needed to build and maintain a network that could deliver power during peak demand - typically winter evenings.
Under the new fee structure home generators would still save about $150 to $190 a year in lines charges.
"We have to build our network to meet peak demands on the coldest winter night, when solar customers need the network as much as any other customer," he said.
"Solar reduces total annual consumption and therefore under old prices these customers reduce their contribution to the cost of providing the service they require to keep the lights on during winter, with other customers bearing this cost or subsidising these customers in the long-term."
Solar hot water heating systems and gas heating systems were not targeted in the new structure. Mr Strong explained that these systems had a different impact on the network as they removed consumption from evening peaks.
As gas was predominantly used for cooking or heating in winter it reduced demand on the network and network costs.
Mr Strong anticipated that solar customers would be upset about the reduced subsidy. The increased charge is for new installations while existing customers will stay on their current rate until March 2019.
"We are however surprised that this legitimate pricing decision has been made a political football by the solar installation lobby in an effort to divert attention from the questions recently put to the industry, and endorsed by the Parliamentary Commissioner for the
Environment about solar's marginal environmental benefits in New Zealand," Mr Strong said.
The Electricity Authority said New Zealand still took a "historical approach" to pricing structures and service-based pricing could provide more efficient prices.
However it said Unison was out of step with its recommendations.
The new prices were not related to the services it was delivering, the authority's chief executive, Carl Hansen said.
"Our approach would increase choices for consumers. Unison's approach provides no additional choice of services for consumers."
Mr Strong said it was not possible to move to the authority's preferred pricing approach as there wasn't the necessary infrastructure, such as complete roll-out of smart meters, which was not under Unison's control.
Mr Strong hoped the company would progressively transition so that consumers were supported to make cost efficient decisions and invest in emerging technologies such as solar panels, electric vehicles and LED light bulbs.