China's migrant workers are becoming an "urban underclass," due to economic exploitation and residency rules that deny them access to medical, housing and education benefits, according to a report released by Amnesty International, AP reported. Workers from China's rural areas are forced to work overtime and are fined for being late or not meeting production quotas. Pay is also routinely withheld to keep migrants from changing jobs, a practice that has helped keep wages down despite rising demand for workers. Amnesty said that while migrants are allowed to apply for temporary residency, they must pay extra for schooling and rarely receive insurance or access to subsidized housing. Chinese officials and legislators have said they are debating how to overhaul the residency system but no timetable has been set to replace the current model.