For 17 years, Kearney & Trecker Corp. employees worked five seven-and-a-half-hour workdays, and the company paid overtime for overages. When its collective-bargaining agreement with Lodge 76 of the International Association of Machinists (plaintiff) expired, the company wanted a standard 40-hour workweek. When the company announced the new policy unilaterally, union members refused to work more than seven-and-a-half hours a day or 37 and a half weekly. The company filed an unfair-labor-practice charge, but the National Labor Relations Board (NLRB) dismissed it. The company also filed a complaint with the Wisconsin Employment Relations Commission (WERC) (defendant), claiming the refusal to work overtime violated state labor laws. The union requested dismissal based on federal preemption. WERC refused, reasoning that the National Labor Relations Act (NLRA) neither protected nor prohibited concerted refusals to work overtime and issued a cease-and-desist order. After the Wisconsin appellate courts affirmed, the Supreme Court granted review.