Homeowners across the country are installing solar panels in record numbers, getting their power from the sun and relying less on their local utility grids. Federal and state agencies have subsidized the shift to carbon-free renewable energy, but now some utilities are fighting back with threats to punish solar adopters with higher fees and taxes.

In Arizona, Tucson’s local utility has asked for approval by the state’s power commission on a plan to raise its monthly prices and charge fees, penalties and other charges to homeowners who have installed rooftop solar panels, according to Fox News. The Tucson Electric Power company says that since solar users make less use of the local grid, they end up paying less for its upkeep, unfairly shifting those costs to other customers.

Similar fights are occurring in other states, such as Oklahoma and Utah. In Utah, the state’s Public Service Commission is considering a plan to charge solar users a “sun tax” if they install rooftop solar panels. Some rooftop solar systems are so efficient that they produce excess power on sunny days, which the homeowner gets credit for when the excess goes back into the grid at night.

The state’s largest utility, Rocky Mountain Power, has argued that such customers should be paying more for the use of the fixed parts of the electricity grid such as wiring and utility poles. The company proposed the “sun tax,” but to date the Public Service Commission has not approved the plan, instead calling for a cost-benefit study of the adoption of solar power.

National environmental groups like the Sierra Club defend the homeowners’ rights to make use of the local grid, as any other utility customers do. Other solar proponents agree. As one solar advocate noted, utilities don’t charge more to rural customers or seasonal customers, despite the higher or fluctuating costs to bring them electricity via the grid. They say that the proposed fees or taxes on solar users is unprecedented and unjustified.

They also note that any cost calculation must take into account the environmental benefits of solar, which ultimately lead to lower costs for all customers. They note that renewable energy sources add value by ending carbon emissions, reducing power losses, and eliminating the need to build new power plants.