Tom did ask a good question though, Loren. Why else would they hold the passports if not an attempt to control these women? Could be identity theft I guess. Could be other things. But trafficking sure does seem to top the list to me. As I said above, it isn't conclusive, but its pretty good evidence.
I do agree it's an attempt to control them. It's a useful tactic if they are illegals, it's nowhere near strong enough if they are truly trafficked. Hence I see that as more evidence they are simply here illegally.
Smuggling human beings is a primary characteristic of trafficking.
Add in confiscation of passports, which as you admit is an effort to control (and I will add, an extremely effective tool to control)
Make it difficult for persons to freely leave the place of employment and to have all of their movements outside of the place of business under the control of other employees/business owners
Move these persons periodically, without their consent or input or control
And it really is trafficking. Especially when you consider that they are moved from site to site at the employer's/owner's will and to hide the nature of the business model and also to control the 'employees'/slaves. Because, really that's what you are talking about: persons with so little control over their work or life conditions, places of work/domicile, ability to move, coupled with extremely poor compensation and high rates of 'rent' and 'transportation' and so on and what you really have are slaves that you can throw a few bucks at once in a while and you can make disappear whenever you want by moving them to a different location--or by killing them. Simply moving them often enough that they aren't able to develop a special relationship with clients is probably enough, though.
Trafficking is notoriously difficult to prove because it is notoriously difficult to get witnesses who are moved frequently and who may or may not have much proficiency in English, may come from an area where police are notoriously corrupt, meaning they have little reason to trust the police and given threats against family members back home, it's pretty hard to locate victims or to get them to testify.
Trafficking happens with Americans, too. Usually very young girls who are runaways. I suspect also young boys but I have read much less about that. Girls are often first befriended, then perhaps seduced, offered protection, and if they 'act up,' the threats begin. Against them, sometimes against family back home. They have little access to money, little freedom of movement. Little control over any aspect of their lives. They are moved from place to place: trafficked.