Season 158 - Day 13 of 14

What is the name of the system used in in many middle eastern countries in which migrant workers must have an in-country sponsor, usually their employer, who is responsible for their visa and legal status to gain a work permit?
Human rights organizations criticize the practice for creating slave like conditions, because the employers can prevent the migrant workers from changing jobs and in many cases take away their passports, thus preventing them to go back to their home countries.