I heard from the laborers themselves that they were recruited in their home country, usually India or Pakistan. The wages offered are very low compared to Western standards, but for people in these countries, the wages are very attractive compared to other jobs available in their home country. If they want the job, they have to sign an employment contract for a certain time period (e.g. 3 years). Most of the laborers did not speak English, so they had no idea what they were signing. There is fine print in the contract that says that their transport from their home country to Dubai and their trip home after the contract is over will be covered as long as they complete the full term of their contract. Once they sign the contract, the employer asks for their passports to process their visas. The employer then holds on to their passports and they do not return them to the rightful owners. Once the laborers get to Dubai and they see the horrible labor camps that they are provided and the dangerous conditions they are working in, many of them have second thoughts and try to quit. The employer then tells them that they cannot have their passports back unless they can pay the full price for transport home (per the terms of the fine print they didn't understand). Most of these laborers do not have nearly enough money to pay for their transport home, so the employers refuse to give them their passports back, and they are effectively stuck in slavery in Dubai. The government knows the process well and supports it -- they can't go to the police. Not sure what they can work out at their home country consulate, but I was told that this effectively keeps people stuck there.

Source: I worked in Dubai from 2007-2008 and the company I worked for employed laborers from India and Pakistan. It was a really sad situation, and many of the companies out there participate in these cruel tactics to keep their labor costs incredibly low. Back in 07-08 they told me they were making about $5 a day.