Eversource filed a lawsuit on Thursday challenging state regulators’ decision to cut more than $500 million from the company’s reimbursement for responding to a series of powerful storms in Connecticut.

The lawsuit, which was filed in Superior Court in New Britain, claims that the Public Utilities Regulatory Authority ignored state law and its own precedent by rejecting the company’s request to be paid interest on the costs it incurred responding to storms, while waiting several years for regulators to determine whether those expenses were necessary.

Because Eversource had to finance the cost of its storm-related expenditures, the lawsuit argued the company is now entitled to recoup that interest.

“The ramifications of this appeal are significant and will help to provide clarity regarding the legal principles which dictate our ability to finance storm cost recovery for customers who demand that their power be restored as fast as possible with minimal interruption,” Eversource spokeswoman Jamie Ratliff said in a statement Thursday.

The lawsuit also challenged PURA’s decision to cut roughly $7.7 million in crew costs from Eversource’s reimbursement, which the company said was based on faulty methodology.

A spokesperson for PURA declined to comment on Thursday.

PURA reached its decision in the storm costs case in July, approving more than 90% of Eversource’s request to be reimbursed for nearly $1 billion worth of expenses that the company said it incurred while responding to dozens of “catastrophic” storms between 2018 and 2023. Those storms, which each cost the company more than $4 million, are treated differently than smaller, more routine storms, which Eversource is expected to respond to using money from its base rates.

While PURA sided with Eversource in allowing most of those expenses to be reimbursed, regulators denied the company’s request to be paid an additional $400 million in interest while the case was adjudicated. (PURA also cut about $100 million in actual expenditures from Eversource’s reimbursement, though some of those costs may be recovered in the future if the company provides additional supporting evidence.)

The decision further said that Eversource is only entitled to earn interest on storm costs once those expenses have been reviewed and deemed prudent — meaning from the date of the final agency’s final decision until the costs are actually repaid.

In a statement on Thursday, Attorney General William Tong said that Eversource itself was to blame for the long wait in getting paid for its storm costs.

Eversource filed its initial request for reimbursement in 2023, several years after the earliest expenses in the case were incurred. Tong said the company then dragged its feet responding to questions about those costs from his office and the Office of Consumer Counsel, filing motions for extensions that resulted in more than 1,000 additional days of delay.

“The workers who restore our power following catastrophic storms deserve compensation and gratitude — that is without doubt,” Tong said in a statement. “PURA was right to approve those costs. But that wasn’t enough for Eversource. This fight is about hundreds of millions of dollars in unjustified interest payments for years where they had never even asked for recovery. In the real world, when kids hand in late homework, they don’t get bonus points. We’re going to fight this appeal with everything we’ve got to ensure Connecticut families aren’t stuck paying this outrageous, unaffordable and unjustified demand.”

Claire Coleman, who heads the OCC, also criticized Eversource’s decision to file an appeal of PURA’s final decision despite receiving the majority of its request. Her office, she noted, sought an additional $171 million in cuts based on its review of Eversource’s expenses.

“At a time when families are struggling to pay their monthly electric bills and make ends meet, Eversource seems more interested in bleeding customers dry and draining state resources than accepting the outcome of a three-year regulatory review,” Coleman said in a statement. “Instead of moving forward and focusing on serving customers, Eversource is choosing to bankroll costly, meritless appeals, diverting time and attention from the critical work of addressing Connecticut’s energy affordability challenges.”

During a call with investors last month, Eversource chief executive Joe Nolan said he was “very, very pleased” with PURA’s decision to approve the vast majority of the company’s expenditures in the storm costs case. He also signaled that the company would continue its fight over interest payments, or “carrying charges.”

“Listen, we asked for these carrying charges, carrying charges are important,” Nolan said. “We feel they owe us the money, and that’s not over yet.”

The storm costs case is separate from Eversource’s request for a double-digit rate increase, which remains pending before PURA.

However, Eversource has sought to finalize its storm costs in time to allow those charges to enter customers’ bills around the same time that new rates go into effect next July. As a result of a new law passed by the Connecticut legislature in 2025, utility companies are allowed to “securitize” their storm costs, essentially borrowing money at low interest rates in order to lessen the impact on customers.