Eversource Energy has spent $4.9 million on legal expenses and expert witnesses building the case for a massive rate increase, and now the company wants customers to pay for it.

Massachusetts typically allows utilities to seek customer reimbursements for the work needed to get approvals for new electricity and natural gas rates. But Attorney General Maura Healey’s office is objecting because the amount sought by the company is unusually large.

Healey’s team on Friday filed a request aimed at prompting Eversource to provide details about the expenses to the state Department of Public Utilities.

“Eversource’s robust year-to-date earnings and its unprecedented spending on this rate case confirm what our office has been saying for months — the rate increase is unnecessary and unjustified,’’ a Healey spokeswoman, Chloe Gotsis, said in a statement. “Electric customers deserve a decrease.’’

Healey would also prefer these kinds of expenses be split 50/50 between ratepayers and Eversource shareholders.

The company says the latest version of its request, if approved by state regulators, would increase costs for its Massachusetts electric customers by about $91 million annually. Eversource is also seeking what’s known as a performance-based increase that could bring in tens of millions more each year.

Statistics compiled by the attorney general’s office show that utilities have spent an average of $1.3 million on legal and administrative expenses related to rate requests in the state since 2010. The Eversource request, which became public this week, is roughly twice the size of the next largest reimbursement approved by the state utilities agency over that time, Healey’s office said.

“It’s unfortunate that ratepayers are being asked to pay such exorbitant amounts so the company can get its rate case approved,’’ said Charlie Harak, a senior attorney at the National Consumer Law Center who focuses on energy issues. “This is on the unreasonable end of the spectrum compared to other rate cases in Massachusetts, and perhaps even rate cases around the country.’’

Eversource spokeswoman Caroline Pretyman defended Eversource’s request, saying that this is not an ordinary rate case. The company, which has dual headquarters in Boston and Hartford, is in the process of combining legacy NStar Electric and Western Massachusetts Electric Co. rates. So this is essentially a rate request for two utilities, not just one, Pretyman said.

Throughout this process, which has taken the better part of a year, Eversource has submitted responses to more than 2,500 data requests, and participated in 13 public hearings across the state and 19 days of evidentiary hearings, Pretyman said.

She also noted that Eversource made a significant change midway through the review to better balance the costs between its Eastern and Western Massachusetts regions. That change alone added nearly $1 million to Eversource’s regulatory costs.

The Department of Public Utilities is expected to make a final decision on Eversource’s rate request by the end of the month.

Jon Chesto can be reached at jon.chesto@globe.com.