Attorney General Kris Mayes and two environmental organizations filed complaints against the Arizona Corporation Commission on Thursday over its June decision to exempt an energy company from an environmental review of its power plant expansion. 

The ACC voted in June to reverse an order from the Arizona Power Plant and Transmission Line Siting Committee requiring UniSource Energy to obtain a Certificate of Environmental Compatibility for its proposed expansion of the Black Mountain Generating Station near Kingman.

Mayes’ office filed the complaint in Maricopa County Superior Court, saying the commission “misinterpreted key terms and made erroneous conclusions” in its decision. 

“Arizona’s energy projects must remain accountable under the law in order to protect communities and our environment,” Mayes said in a statement. 

Mayes is asking the court to throw out the commission’s ruling and order commissioners to deny UniSource’s request to forgo environmental review of the plant expansion. 

Under state law, utility companies must receive a Certificate of Environmental Compatibility, known as a CEC, for power plants with generators of 100 megawatts or more. UniSource argued that the expansion project would add four generators that are 50 megawatts each and should not require a CEC, despite the total wattage of the expansion exceeding 100 megawatts. 

Several groups, including Western Resource Advocates, the Sierra Club, Arizona Solar Energy Industries Association and the attorney general’s office, asked the commission to rehear the case, saying the decision went against decades of precedent. The commission did not respond to the request, effectively denying it.

Western Resource Advocates and the Sierra Club both filed motions similar to the one filed by Mayes. 

“The requirement that utilities obtain a certificate of environmental compatibility is an important part of Arizona’s regulatory process,” said Emily Doerfler, an attorney for WRA, in a written statement. “The Commission’s decision to gut this requirement disregarded decades of precedent, is unsupported by evidence and contrary to Arizona law.”

In the lawsuit, Mayes also accuses the ACC of considering evidence that was “not permitted by law” in order to make its decision, thus creating “ambiguity in the law.”

The commission has defended its decision, saying it was only following language in state statute that left little room for interpretation.

“The Commission followed the letter of the law as written,” said Tom Van Flein, the commission’s general counsel, in a written statement on Friday. “Policy advocates wanted a different interpretation for policy reasons. That remains the purview of the Legislature.”

The advocacy groups have dismissed that reasoning, saying it doesn’t explain why the commission had previously ruled the opposite for nearly 50 years. They say the Legislature made the intent of the law quite clear by including a policy statement for the statute when it was passed. 

It’s unclear when the court will make a decision on the complaint. If the case is unresolved before Election Day, the commission could have a new makeup if the court sends the decision back for a vote.