Work, especially for vulnerable, exploited populations, is not voluntary. Particularly when we talk about pseudo-slavery tactics used on migrant workers or other vulnerable populations.

There's a reason companies will often progressively move down to poorer, more vulnerable populations for their labor. Those people are much easier to exploit. We even see this in the US, to an extent. Tyson recently had a debacle where they threatened their (knowingly undocumented) workers with ICE if they attempted to unionize. To call this "voluntary" is willfully ignorant, at best.