The union representing 10,000 workers for three St. Louis grocery store chains has filed a complaint with the National Labor Relations Board. Union workers are threatening to strike next week against Schnucks Markets, Dierbergs Markets and Shop ‘n’ Save Warehouse Foods. The companies have threatened to hire temporary workers if there is a strike. The union says it’s unfair for the companies to be offering replacement workers $12.50 an hour when a union worker has to be employed for five years to get that much. Representatives of the grocery chains say the difference is that temporary workers will not have health insurance and pension benefits and union workers do.