Answer:
A mediator cannot be called as a witness.
Step-by-step explanation:
A mediation process, like the one held between the labor union and the company, is confidential. Everything that is discussed in a mediation is considered confidential, and that involves all the parties that participated in it. In this case, a supposed agreement was reached and that is why the union is suing the company, but the details of what was discussed in the mediation process cannot be made public.