ST. LOUIS – Approximately 3,500 union workers at three Boeing plants in St. Louis, St. Charles, and Mascoutah, Illinois, rejected a four-year labor agreement with the aerospace giant on Sunday, the final day of a proposed “cooling off” period before a strike goes into effect at midnight.

Members of the International Association of Machinists and Aerospace Workers District 837 say the company’s latest offer still falls short of what they believe is fair compensation and job security for the skilled work they do.

Union members had previously rejected Boeing’s initial offer on July 27.

“IAM District 837 members have spoken loud and clear; they deserve a contract that reflects their skill, dedication, and the critical role they play in our nation’s defense,” IAM District 837 Directing Business Representative Tom Boelling said. “We stand shoulder to shoulder with these working families as they fight for fairness and respect on the job.”

The latest proposal included the removal of the controversial alternate workweek schedule, a $0.50 per hour raise for top-scale mechanics, changes to the pension multiplier that would make a $10 multiplier effective in year one, a $5,000 ratification bonus, and continued vacation, sick leave, and healthcare benefits.

This past Thursday, Boeing presented a modified contract to the union. It removed the alternate workweek schedule first proposed, added a 50-cent per hour pay raise for mechanics at the top of the pay scale, and changed a $10 pension multiplier, making it effective in year one of the new deal.

The $5,000 ratification bonus, vacation, sick leave, and healthcare included in the first offer are still included. Boeing claims the average annual wage in this latest offer jumped from $75,000 to $102,600, amounting to what it called “40% average wage growth.”

“We're disappointed our employees rejected an offer that featured 40% average wage growth and resolved their primary issue on alternative work schedules," Dan Gillian, Boeing Air Dominance vice president and general manager and senior St. Louis site executive, said. "We are prepared for a strike and have fully implemented our contingency plan to ensure our non-striking workforce can continue supporting our customers.”

The IAM Union represents 600,000 active and retired members in North America. Its members are responsible for manufacturing and maintaining military aircraft and weapons systems, including the F-15 and F/A-18 fighter jets. Leaders from the IAM say they’re ready to hold the line until a deal is reached that honors their experience and contributions to national defense.

"They're not happy with how they did the wage increase because it's not a general wage increase for everybody," said Chris Albin, Assistant Directing Business Rep, IAM Local 837. "There were some conditional things with it. So they tout it's a 40 percent increase, but it's really only a 12 percent increase for everybody over the four years."

This is the first time boeing defense workers have been on strike since 1996. As of Monday morning, Boeing had not announced any further plans to return to the bargaining table.

CORRECTION: A prior version of this story had a mentioned an incorrect average wage increase percentage. That number has been removed. We regret the error.