Lockheed Martin [LMT], union representatives and federal mediators began discussions yesterday in an attempt to resolve a nearly two-month old strike by machinists at the company’s fighter jet making facility in Fort Worth, Texas, and two other locations.

The International Association of Machinists and Aerospace Workers said this week that they accepted an invitation from the Federal Mediation and Conciliation Service to explore a settlement to the strike that began on April 23. The union employees support the F-35 and F-16 fighter jets and other programs at the three locations.

The crux of the disagreement is over Lockheed Martin’s proposal, which was rejected by 93 percent of the voting union members, to offer new workers a defined contribution plan instead of the traditional defined benefit pension plan. The company has maintained that the defined contribution plan has been accepted by other employees at its company.

The IAM said the proposed pension plan would require higher deductibles and no cap on annual out-of-pocket expenses.

Lockheed Martin hasn’t mentioned what impact, if any, the strike could have on its second quarter financial results, which will be posted in late July. A spokesman for the company’s operations in Fort Worth told Defense Daily that they still plan to deliver 30 F-35s this year. Since the strike began, there have been 40 F-35 flight tests, three aircraft have been delivered and seven are ready for government acceptance, he said.

Lockheed Martin is keeping its factory running with around 1,600 workers, most of whom are salaried employees in Fort Worth, but also a contingent of temporary workers and 50 employees from other company locations to perform specialized tasks such as aluminum tube welding. This production workforce is working six and sometimes seven days a week with shifts of 10 or 12 hours, the spokesman said.

The production workforce at Fort Worth is about one-third of the normal factory workforce, the spokesman said.