Thousands of members of a union representing Boeing defence industry workers in the US states of Missouri and Illinois will go on strike after rejecting a revised proposal for a new contract.

“Approximately 3200 highly skilled IAM Union members at Boeing facilities ... voted on Sunday, Aug 3, 2025 to reject a modified four-year labour agreement with Boeing,” the International Association of Machinists & Aerospace Workers said.

“A strike will begin at midnight on Monday, August 4.”

Members of the union’s local chapter “have spoken loud and clear, they deserve a contract that reflects their skill, dedication, and the critical role they play in our nation’s defence”, IAM District 837 representative Tom Boelling said.

The American aerospace giant’s initial proposal, which included a 20% wage increase over four years and more holiday time, was rejected a week earlier.

The new offer doubled the wage increase, according to Boeing.

“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 senior St Louis, Missouri 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 storied company has been in crisis since last year because of production quality issues and a seven-week strike that crippled two of Boeing’s major assembly plants.

IAM is one of North America’s largest unions, representing about 600,000 members in aerospace, defence, shipbuilding, transportation, health care, manufacturing and other industries.

– Agence France-Presse