Land Air Delivery, Inc. (defendant) employed drivers who belonged to the Teamsters Union and others who worked as independent contractors. When the union went on strike, the company initially used existing contractors, replacement employees, and other staff to continue operations. But after three months, the company filled all driver positions with additional independent contractors. The parties had disputed the use of independent contractors in the past, but the company did not discuss the decision with the union. When the strike ended and union drivers wanted to return to their jobs, the company said it had no work for them. The union filed unfair-labor-practice charges under the National Labor Relations Act (NLRA). The National Labor Relations Board (NLRB) found that the NLRA required bargaining with the union before subcontracting out unit work, and the company appealed.