Lines company Unison says solar electricity users connected to its network were subsidised by other power consumers, necessitating a lift in charges.
On Friday it announced higher fees for customers who use a combination of solar energy and the electricity grid in Hawke's Bay, Taupo and Rotorua. It is the first lines company in New Zealand to levy the extra charge, typically from solar generation.
The Green Party called on the company "to join the 21st century". Napier MP Stuart Nash said it was "a backwards approach" that set a bad precedent.
"If consumers move their appliances from electricity to gas, there is the same effect of falling electricity usage, but power companies don't charge them more for their electricity," he said.
"Unison should be working with customers who go solar, rather than against them. The risk is that treating customers like this will only encourage them to move onto emerging technologies like batteries that will move them off-grid. That would increase lines charges for everyone else."