'Brothels on wheels' in New York City
16 May 2012 Last updated at 16:17 BST
Many trafficking victims are smuggled from Mexico to New York City, where they are made to work 12-hour shifts, servicing 25-30 men a day.
Some women live in brothels, only leaving when their pimps move them to a new location.
The National Trafficking Resource Center estimates each brothel makes on average $5,250 a week per woman.
Other women have their services advertised on what are called "chica cards." They are delivered to a customer's house by a driver.
Frequently the women are assaulted by their pimps and their customers.
Produced by the BBC's Laura Trevelyan and David Botti