You are a labor attorney advising a union that is considering a strike against the unionized employer at its primary location, a large manufacturing concern.  There is a fence surrounding the entire location and the only access is through two gates cut through the fence.  Is it possible that it will be an unfair labor practice to picket at one of the gates?  What information do you need in order to advise the union as to which of the two gates it may or may not picket under NLRA case law?