Hammond, a mediator, assisted in negotiations between a union and a company. After mediation, the union declared that an agreement had been reached. The employer denied that an agreement had been reached and refused to sign the union contract. The union filed an unfair labor practice complaint with the National Labor Relations Board. The company claimed that it had the right to call the mediator as a witness in the unfair labor practice complaint. Could the mediator be called to give testimony in the case? [National Labor Relations Board v. Joseph Macaluso, Inc., 618 F.2d 51, 9th Cir. (1980)]