A debt-collection firm working for National Grid violated federal law when it made unauthorized cellphone calls to late-paying customers, using automated phone systems, according to a new federal lawsuit.

The suit, filed Monday on behalf of Jarrett Jenkins of West Hempstead, alleges the debt-collection firm, NCO Financial Systems, in 2011 used automated-dialing and voice-messaging systems to improperly call and leave messages on his cellphone, in violation of U.S. Telephone Consumer Protection Act.

The law makes it illegal to use automated dialing systems to call cellphones except for emergency purposes or with the prior consent of the phone user.

The suit names National Grid USA, its London parent company and its numerous wholly owned operating subsidiaries, including KeySpan, Niagara Mohawk and National Grid Generation, as defendants. NCO is not a named defendant. Jenkins previously filed suit against NCO, charging the company improperly accessed his credit records. Calls to NCO were not returned. Aaron Easley, an attorney for NCO, declined to comment.

National Grid spokeswoman Wendy Ladd said the company had not been served with the suit, and declined to comment.

The suit, filed in U.S. District Court in Central Islip, charges NCO called Jenkins' cellphone repeatedly between March and September 2011 using automated equipment to make the call and leave messages without his consent. Records confirming the calls were produced in Jenkins' case against NCO, according to the suit.

Southold attorney Joseph Tusa filed the suit seeking class-action status on behalf of hundreds of thousands of potential plaintiffs who received calls from any debt collector used by National Grid that employed the same practices, court papers say. The suit seeks $500 per violation, plus tripled damages. Tusa declined to comment.

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While the calls weren't made by National Grid staff, the suit charges the company is liable because it hired NCO to collect its debts. The Long Island Power Authority, which was operated by National Grid in 2011, isn't named in the suit.

The suit alleges the debt-collection firm obtained customers' cellphone numbers by practices known as "skip tracing" and "number trapping," which records customer numbers that appear on caller ID systems.

"The hardware and software used by NCO has the capacity to generate and store random numbers, or receive and store lists of telephone numbers, and to dial those numbers, en masse, in an automated fashion without human intervention," according to the suit.

Reached on his cellphone, Jenkins also declined to comment.