U.S. residential solar installer SolarCity has filed a lawsuit against Arizona utility Salt River Project, accusing the utility of violating antitrust laws. The lawsuit, filed in Arizona federal court, alleges that Salt River Project’s new electricity rates penalize customers who choose to go solar. SolarCity said that SRP was trying to “destroy the competitive threat” from solar companies.

SolarCity Corp Sues Arizona Utility Salt River Project

SRP’s new pricing plan punishes solar customers

The lawsuit is part of a growing conflict between rooftop solar installers and Arizona utilities over how traditional utilities will preserve revenue as more customers go solar and pay less to their utilities. SolarCity says SRP’s new pricing plan adopted on February 26 will “punish” customers who generate their own power.

Most rooftop solar systems are not connected to batteries. So, solar customers typically send the output to the grid and receive a credit on their monthly electricity bills. Adding extra fees would offset the economic benefit to the customer, said SolarCity in a blog post. Under the new pricing plan of SRP, customers who don’t have solar panels will be charged a minimum of $20 per month.

SolarCity’s new applications decline 96%

But for people who generate their own electricity through solar panels, the minimum distribution charge has been set a $32.44. Further, the Salt River Project will impose a demand charge based on power usage. According to court papers, the demand charge would range between $30 in winter to $125 in the summer. Non-solar customers don’t have to pay demand charges.

The new pricing is scheduled to become effective in April. It was first proposed in December last year. The new charges will apply only to customers who installed solar systems after December 8. SolarCity said new applications for rooftop solar declined 96% in SRP’s service territory after the utility came up with the new pricing policy in December. SolarCity has approximately 7,000 customers in SRP’s territory.

SolarCity shares fell 0.58% to $49.97 at 11:16 AM EST on Wednesday.