Thousands of aerospace workers could find themselves temporarily out of work if the U.S. government shutdown continues.

Sikorsky Aircraft, which produces the UH-60 Black Hawk Helicopter, plans to furlough 2,000 workers at three plants on Oct. 7 due to the absence of Defense Contract Management Agency (DCMA) inspectors who audit and approve the manufacturing of military products. Sikorsky parent United Technologies warns that another 2,000 workers could be furloughed from its Pratt & Whitney and Aerospace units.

Other defense contractors were drawing up similar plans. “A number of our member companies have notified me that if this shutdown continues, which is affecting all of the [Defense] Department functions involved in contracting, it will force them to furlough thousands of workers,” Aerospace Industries Association President Marion Blakey told Defense Secretary Chuck Hagel in an Oct. 3 letter.

Blakey stressed how much contractors rely on DCMA approvers. “The manufacturing process must stop if these inspections and certifications are not performed,” she wrote. “Within days many of our members will have no choice but to halt certain defense manufacturing production and furlough employees indefinitely, absent government guidance and payment.”

By Oct. 4 other companies including Lockheed Martin were also preparing for furloughs. On Oct. 4, Lockheed told employees that about 3,000 workers would be furloughed on Oct. 7. If the shutdown continues, that number could increase, according to a memo from Marillyn Hewson, Lockheed’s president and CEO.

“We expect the number of employees affected by the shutdown to grow as we experience contractual actions and the impact of furloughs among DCMA and other customer inspectors across our business and our suppliers’ businesses,” Hewson wrote.