More than 3,200 Boeing union workers in Missouri and Illinois are on strike following the rejection of a four-year labor agreement with the aerospace company.

The workers who assemble fighter jets turned down a four-year contract that would have raised the average wage by roughly 40% and included a 20% general wage increase and a $5,000 ratification bonus, according to Reuters. It also included increasing periodic raises, more vacation time and sick leave.

“We’re disappointed our employees in St. Louis rejected an offer that featured 40% average wage growth,” Dan Gillian, Boeing vice president and general manager of the St. Louis facilities, said in a statement to Reuters.

Boeing Defense said it was ready for the work stoppage and would implement a contingency plan that uses non-labor workers.

INSIDE AMERICA’S 6TH-GEN ARSENAL: B-21, F-47, AND THE FUTURE OF AIR DOMINANCE

“IAM [International Association of Machinists and Aerospace Workers] District 837 members build the aircraft and defense systems that keep our country safe,” IAM Midwest Territory General Vice President Sam Cicinelli said in a statement. “They deserve nothing less than a contract that keeps their families secure and recognizes their unmatched expertise.”

The union said in a press release that its workers “assemble and maintain advanced aircraft and weapons systems, including the F-15, F/A-18, and cutting-edge missile and defense technologies.” 

BOEING DIVISION HANDLING TRUMP FIGHTER JET PROGRAM BRACES FOR STRIKE AFTER UNION REJECTS CONTRACT OFFER

IAM represents 6,000 active and retired members across the U.S. and Canada.

Boeing did not immediately respond to a FOX Business request for comment. 

Boeing’s defense division has been expanding operations in the St. Louis region to support the production of the U.S. Air Force’s new F-47 fighter jet, after securing the Pentagon contract earlier this year.

In March, President Donald Trump formally designated the F-47 as the U.S. Air Force’s next-generation air superiority fighter, positioning it at the center of the Next Generation Air Dominance program that is expected to replace the aging F-22 Raptor, according to the Congressional Research Service, a nonpartisan agency that supports Congress.

FOX Busines’s Bonny Chu, Danielle Wallace and Reuters contributed to this report.