Lockheed Martin hired temporary workers on Thursday in order to meet the commitments to its customers in lieu of striking employees at its Texas plant.

The Pentagon’s top supplier of F-16 and F-35 aircrafts has brought around 10 workers to its plant in Fort Worth, Texas, from a small contractor. Another 50 to 60 are expected to be added next Tuesday, according to Joe Stout, Lockheed’s spokesman, in an email to Reuters.

“The transition to a defined-contribution pension plan for new hires is an industry standard, which we have successfully implemented in a number of recent labor agreements, and is a necessary action that will help us deliver greater affordability to our customers,” wrote Lockheed Executive Vice President Larry Lawson in a memo on Thursday.

On April 22, members of the International Association of Machinists and Aerospace Workers have refused Lockheed’s offer and voted to go on a strike. Around 3,300 members are continuing in its fifth week. If the strike lasts one more week, it could be the longest in the history of the Forth Worth plant, replacing the six-week strike record in 1946 against the plant’s operator Convair.

“We feel strongly that we made a fair and generous offer to the IAM members, but we have a fundamental disagreement on retirement savings,” wrote Lawson in the Thursday’s memo.

However, the decision of using temporary workers in producing a sophisticated aircraft has been criticized by the union.

“No one can believe there is ANYONE already qualified to work on the F-35 that isn't already working for Lockheed Martin. It's the most unique aircraft in the world,” wrote the union on its blog, goiamtexas.com.

“Lockheed will waste millions to hire unskilled and untrained workers to make a silly show that won't produce anything.”

Meanwhile, Stout said Lockheed achieved its second “customer acceptance” on Thursday of F-16 jet since the strike began.