NorthWestern Energy must disclose more information before the Montana Public Service Commission considers its application seeking more money from its customers – $156.5 million more in base revenue from electricity costs alone.

On Tuesday, the Public Service Commission said the utility had provided additional information on its pending request for increased revenue in response to a PSC notice earlier this month.

However, NorthWestern has still not adequately explained its studies on “cost of service” or how costs are allocated to different customer groups, such as residential or commercial customers, regulators said at their meeting on Tuesday.

In a statement after the meeting, PSC President James Brown said the commission could not proceed until NorthWestern complied with the law and provided more information.

“In order for the Commission to review a rate case, the PSC requires very specific economic and business data from any monopoly applicant seeking to adjust the rates it charges Montana consumers,” Brown said. “Compliance with these rules is essential for the PSC to do its regulatory work. To date, NorthWestern has failed to meet this critical standard of information.”

In the past, various groups have argued before the Public Service Commission not only over how much additional revenue NorthWestern should receive under the fee arrangement, but also over which classes of customers should pay.

At least some parties from previous proceedings also want to participate in the current proceedings.

In its own motion to intervene, Walmart stated that energy costs represented a significant portion of its operating costs. Walmart has already argued that it should be allowed to have a say in determining the right rate of return for NorthWestern, including any necessary “adjustments” to the cost studies.

A group of industrial energy customers, known as the Large Customer Group, also filed a motion to intervene. The group includes Calumet Montana Refining, REC Silicon and Stillwater Mining Co.

The PSC regulates monopoly utilities in Montana.

In the recent rate dispute with NorthWestern, some parties argued that residential customers should pay the bulk of the utility’s sought-after revenue increases. However, the Large Customer Group argued that residential customers would continue to be subsidized.

Regarding NorthWestern’s missing information in the current application, Commissioner Randy Pinocci wanted to know whether Public Service Commission staff had already identified “such problems” in other applications or whether the deficiencies in the current application were a new one.

The PSC had previously identified “several instances” where the utility’s application did not meet requirements. Responding to Pinocci, tariff analyst Haylee Gobert said other filings had identified “minor deficiencies” but this one had “a higher threshold for deficiencies.”

“This is the first time we’ve seen this,” Gobert said.

According to NorthWestern, the request from a typical residential customer would mean an increase in electricity costs of 8.3 percent and in natural gas costs of 17 percent. However, the energy supplier is also demanding smaller interim increases effective October 1.

As requested, the total amounts include increases in base costs, which are permanent following approval by the Public Service Commission, and a reduction in total pass-through costs, which may change quarterly.

Earlier this month, commissioners declared NorthWestern’s application insufficient and requested more information.

In another attempt to obtain a complete application, the Public Service Commission on Tuesday said by a 5-0 vote that NorthWestern Energy’s application still needs more details to comply with the regulations.

A similar rate dispute is currently underway at Montana-Dakota Utilities, although the Public Service Commission did not request additional information from MDU in a recent preliminary review.

Last month, both MDU and NorthWestern Energy filed applications for higher rates, MDU for natural gas.

In October 2023, the PSC unanimously approved a settlement reached by NorthWestern and several other parties, including Large Customer Group, Walmart, and Montana Consumer Counsel.

This caused interest rates to rise by an amount that was described at the time as “historic” and “unprecedented” – about 28 percent for households and 25 percent for small businesses compared to the previous summer’s rates.