Which is yet another example of why I have such disdain for SAG. It's not like we're talking about a situation where the studio was really trying to avoid hiring union members. We're talking about some producers trying to do something nice for a group of extremely loyal and dedicated fans for one day.
That's not fair to SAG, which I don't believe had any jurisdiction over Extras/Background Actors back in 1979. Before 1992 most background actors in US film and TV were represented by the Screen Extras Guild. SEG members went over to SAG in 1992.