Boeing Co. faces its first walkout at its St. Louis-area defense factories since 1996 after 3,200 members of the International Association of Machinists and Aerospace Workers District 837 voted on Aug. 3 to reject a revised four-year labor agreement and strike starting at midnight on Aug. 4. The proposal would have delivered an average 40% wage gain, including a 20% general increase and a $5,000 ratification bonus, along with additional vacation and sick leave. Union leaders said the package failed to address scheduling concerns and did not adequately compensate workers who assemble the company’s military aircraft and drones. Boeing said it is “disappointed” by the outcome but has activated a contingency plan to keep operations running with non-union staff. The work stoppage threatens production of the F-15 and F/A-18 fighters, the T-7 trainer jet and the MQ-25 refueling drone, programs that are central to the planemaker’s $26 billion defense business. The dispute adds to a series of labor challenges for Boeing, which weathered a seven-week machinists strike at its commercial-jet factories last year. A prolonged shutdown in St. Louis could disrupt deliveries to U.S. and foreign militaries and complicate the company’s efforts to stabilize its operations after recent safety and financial setbacks.