Workers at two Lockheed Martin aircraft plants voted to accept new contract offers last night but employees at a third plant rejected the offer and went on strike from midnight.
Union officials said that workers at two Lockheed plants in California ratified new deals, but employees at the firm's Marietta plant in Georgia voted by 78 per cent to reject their offer and walk off the job.
Bethesda, Maryland-based Lockheed called the Marietta offer fair with the same major economic terms as that supported by the two California plants, and it said the Georgia facility would still operate.
"The Marietta facility will remain open and we will implement contingency plans to support our business commitments to customers," the company's aeronautics unit said in a statement.
Job security remained a concern for the 2,700 rank-and-file union members at the Marietta plant, said union spokesman Mr Bob Wood. The plant has about 7,000 workers.
The defence company and its labour leaders on Friday reached a tentative deal over new contracts for 6,000 workers at the three aircraft plants, which build the cutting-edge F-22 fighter jet and the C-130 transport plane.
The International Machinists and Aerospace Workers - which represents the aircraft assembly workers, maintenance and office staff - said Lockheed had addressed most of the union's concerns over retirement, medical costs and job security.
While union leaders had recommended workers accept the contracts at two California plants, they had not endorsed the contract at Lockheed's Marietta operation.