Employees of a nonunion sanitation company that cleaned meatpacking plants overnight grew upset over their treatment by the company’s safety personnel. One of their supervisors was sympathetic to their complaints. When that supervisor refused to follow a safety manager’s order to discipline an employee, he was fired. This led to a walkout by employees that closed the plant for a day. The dispute was resolved for a brief period when the company agreed to make improvements and to reinstate the fired supervisor. But shortly thereafter, the company determined that it was going to fire a number of supervisors—including the one that had just been reinstated—for their failure to support the company. When word about this got out, a number of employees left their work areas and congregated outside the plant. Some of the employees who walked out to protest the firing of the supervisors were also terminated. Did the employer violate the NLRA?