Jet engine manufacturer Pratt & Whitney said Thursday that declining work is forcing it to lay off about a quarter of its labor force at a repair plant, prompting the workers' union to question whether the company is violating a federal court order barring it from moving jobs out of the state.

The subsidiary of United Technologies Corp. said it will lay off 129 hourly workers at its Cheshire plant, reducing the labor force from 520 to 391.

The International Association of Machinists, which represents the workers, said in a statement that the layoffs "coincide with Pratt's original game plan for emptying the plant" before contract negotiations later this year.

The union said it will meet with its lawyer to determine if the layoffs "represent actions by Pratt in contempt of the court's decision."

The East Hartford company said in a statement that the reduction is in "full compliance" with its contract with the Machinists and the federal court's ruling.

A federal appeals court last month rejected Pratt & Whitney's plan to move 1,000 jobs out of Connecticut. The 2nd U.S. Circuit Court of Appeals in New York upheld a federal judge's February decision that said the company failed to make every reasonable effort to avoid shutting its Cheshire and East Hartford engine repair plants.

The East Hartford plant is still open, and there were no layoffs there.

The Machinists said Pratt & Whitney could save the Cheshire jobs by furloughing workers or reducing overtime.

"We told them, if you're saying this is volume-related you've got to be able to prove it," said James Parent, chief negotiator for the union. "We're taking a look at it."

He questioned the company's claim that work is declining. Hourly employees have been working 10 hours a day, includes two hours of overtime, and have been asked to work Saturdays, he said.

Pratt & Whitney says it will try to minimize layoffs by offering workers a chance to leave voluntarily with severance pay and no-cost dental and medical insurance for up to 12 months. The company also said it will try to transfer eligible employees to vacant jobs elsewhere.

Operating profit at Pratt & Whitney in the quarter ending June 30 was $522 million, up about 12 percent from the same period in 2009. Operating profit was down nearly 14 percent for 2009 as the company felt the impact of the downturn in the commercial airline industry and sharply reduced orders for corporate jets.