This white card on the left-hand side is the "temporary residence" card for the migrant workers in China. Namely, if one Chinese wants to work outside his/her hometown, he/she needs to pay to get the permission to work. Usually, companies will pay it to the authorities concerned in advance, then they get it back by deducting 10-15 RMB from each employee's wage every month. Apparently, it's a kind of discrimination and exploitation. But the "floating" migrant labor force of over 100 million in China has been proven especially difficult to protect and organized. And their desire to make more money than they can earn in rural area makes them easy to exploit.