Migrant workers on the mainland were owed 100 billion yuan in back-pay by last November, despite repeated pledges by senior officials to ensure they are paid on time. The All-China Federation of Trade Union warned yesterday that it could cost as much as 300 billion yuan to recover the back wages. The amount was calculated based on the cost of such things as food, transport, legal costs and time that migrant workers spent trying to recover their pay. The average cost of retrieving back pay was about 4,000 yuan. It was calculated after a year-long survey of 8,000 workers in eight provinces conducted by the Beijing Youth Legal Aid and Research Centre. A China Youth Daily report yesterday said Guo Zenguang , a migrant worker from Hebei , had spent 4,700 yuan and three years trying to retrieve 1,000 yuan in back pay, but he was still waiting. The survey also found that nearly half of migrant workers are owed wages. The country has 150 million rural migrant workers working in urban areas. Due to the low wages, migrant workers have become the mainstay of the labour force in the construction and manufacturing industries. Officials have repeatedly stressed the importance of the back-pay issue. In January, Vice-Premier Zeng Peiyan said all levels of government should try their best to ensure migrant workers received their wages before Lunar New Year. The Labour Ministry's social security division deputy chief, Yu Mingqin, told CCTV in March that it had 'basically solved the issue of back pay for migrant workers from the countryside'. But it has not been resolved for many rural residents. Research Centre lawyer Xiao Weidong said the high cost of recovering back pay was due to workers having to fund court costs and expenses associated with travelling to and from labour departments to report complaints. He said that with the high costs and the length of time for court proceedings - often from 13 to 25 days - workers were reluctant to pursue claims. Mr Xiao said some workers became violent, assaulting bosses or jumping off rooftops to draw attention to their plight. To make sure the migrant workers were paid, the State Council was drafting a Labour Contract Law to complement existing legislation, Xinhua said.