Best I can come up with is that if the conditions are too bad then it’s human trafficking.
In both case they “consent” to do labor, however human traffickees are often tricked into a more casino-like raw deal.
In both cases, it’s not uncommon to not be unable to quit the job.
Source: I know a lot of migrant labourers
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Lack of societal protections, I.e if you illegally enter a country to work and your employer has no responsibility to pay for your labour, your screwed on both ends. Compared to migrant laborers who get ( as far as I know) workers permits which entitles them to societal protections and a degree of assuredness of payment for labour. (I just thought of this on the spot as the best answer to the question.)