“The threat of arrest and deportation is a common tool traffickers use to control their victims, experts say. Even those immigrants who arrive on a legitimate work-related visa have become trafficking victims. These visas usually bind the worker to an employer, who can hold that requirement over their head and even become their trafficker. ‘If employment ends, then so does visa status,’ says Avaloy Lanning, a senior director at Safe Horizon, a New York-based victim’s services agency. ‘The trafficker uses that against them, [saying], if you run then you’re going to be illegal, then immigration is going to pick you up, arrest you and deport you.'”
http://www.usnews.com/news/articles/2013/04/02/modern-slavery-emerging-from-the-shadows_print.html