When people get captured, they get dragged to some kind of portal. They transform into slaves and have one of their arms become claw-like or weapon-like. They are strong but not very fast.
They also seem to keep dragging stuff used as fuel by the aliens. There is some kind of sewer they drag stuff along.
The hero waits in line, is not recognized and purposefully transforms so he can destroy the portal. I do not recall the hero being a very good person, but in the end he does the right thing.