FORT WORTH, Texas (AP) — Striking Lockheed Martin workers are picketing outside of a North Texas plant where the aerospace company makes F-35 fighter jets.

The strike by Machinists Local 776 in Fort Worth began Monday after union members voted overwhelmingly Sunday to reject the company's latest contract offer. The union represents about a quarter of Lockheed Martin's 14,000 workers at the plant.

Lockheed Martin spokesman Joe Stout says the plant remains open and no problems have been reported. He says some employees have been assigned alternate job duties to take over for the striking workers.

Union leaders say the company's proposed changes to the pension plan, health costs and new hires policy were unacceptible.

The company says it believes the offer is fair.