RENTON, WA—Boeing and its largest union, the International Association of Machinists and Aerospace Workers (IAM), continued contract negotiations today after 25 days of strike action involving 33,000 U.S. West Coast factory workers. Talks resumed Monday with federal mediators, but no significant progress was made. The union is demanding a 40% wage increase over four years and the return of a defined-benefit pension. Boeing had previously offered a 30% raise and a performance bonus, but the union found this offer insufficient. The strike has halted production of the 737 MAX jet, along with its 777 and 767 widebody planes.