More than 200 Central Maine Power Co. customers who believe they have been overcharged on their electricity bills have joined a class-action lawsuit against the company.

Lipman & Katz, an Augusta-based law firm, issued a statement Tuesday night announcing that it plans to file the lawsuit Thursday in Cumberland County Superior Court. Napoli Shkolnik, a New York City law firm, and Trafton, Matzen, Belleau and Frenette of Auburn will join Lipman & Katz in the class-action case.

CMP Ratepayers United, which has demanded that the state conduct a more thorough investigation into customers’ complaints of inflated CMP bills, also has been invited to join the lawsuit, said Sumner Lipman, the founding partner of Lipman and Katz.

CMP Ratepayers United has more than 4,800 members.

About 97,000 Central Maine Power customers‘ monthly bills increased 50 percent or more in December, January or February over the same month a year earlier, according to information the company provided to the Public Utilities Commission in April. The law firms contend that another 200,000 customers have been overcharged by up to 50 percent.

“In order to bring relief for these customers and compensation for their overpayment, the law firms have joined resources to bring a class action on behalf of customers of Central Maine Power Company, who have been overcharged,” said Lipman & Katz in a news release.

Gail Rice, a spokeswoman for CMP in Maine, was aware of the lawsuit Tuesday night but said the company had not seen the complaint and could not comment on the matter.

“CMP values its customers and is committed to fair and accurate metering and billing,” Rice said.

Lipman said in an interview Tuesday night that several aggrieved ratepayers will be present when the lawsuit is filed in court Thursday at 1 p.m. Mark Levesque of Scarborough will serve as the lead representative. He was out of state and could not be reached Tuesday night.

“I’ve had more than 200 people come to me seeking help,” Lipman said late Tuesday evening. Lipman said that a class-action lawsuit makes it affordable for CMP customers who might otherwise not be able to pay the cost of hiring lawyers to represent their interests.

“If you are a customer of CMP who has been overcharged, you deserve relief. Many persons have been burdened with bills in excess of $500 per month while others, some on fixed incomes, have suffered hardships trying to pay these bad bills,” the release says. “There are people that did not receive bills for months only then to receive a disconnect notice.”

Lipman said many CMP customers have told his staff that when they contact CMP about a disputed bill they must speak to someone from Texas.

CMP has nearly 550,000 customers in Maine.

Earlier this month, the Maine PUC authorized Liberty Consulting Group of Pennsylvania to expand its audit of CMP’s customer service and communications as well as its billing and metering systems.

Auditors will examine whether CMP adequately responded to customer calls within a reasonable time frame as well as its reaction to complaints about high bills. The PUC is also conducting its own investigation of CMP’s metering, billing and customer service performance.

CMP is a subsidiary of Avangrid, a multinational utility company headquartered in Spain.