Can you tell me the name of this movie about women keeping men as slaves?

Many years ago, probably in the 70’s, I saw a film on TV. A team of scientists get into a tunnel boring vehicle (big van with rock drills on the front to burrow through the ground) and emerge on some unknown other part of the planet. It turns out that the only men there are kept as slaves/breeding stock by the women. The women keep the men drugged at all times, and if they look the women in the face, they’re told in a stern voice, “Eyes down!” Of course, the male scientists are captured and drugged and sold into slavery.