Fifty-one companies in north China's Hebei Province were blacklisted for delaying salaries of migrant workers, local authorities said Tuesday. According to the Department of Housing and Urban-Rural Development of Hebei, the blacklisted companies include 49 construction firms, which were found to have delayed the wages of migrant workers, and two property developers that have affected the payment of migrant workers' salaries by delaying project funds. Eleven provincial construction companies are banned from bidding for new projects and 38 construction companies from outside the province were asked to exit the Hebei market. The two developers are forbidden from taking new bids. Salary delays have been a perennial headache for hundreds of millions of migrant workers, who often lack formal contracts and sometimes go unpaid after their companies report low earnings or declare bankruptcy. On March 6, 21 migrant workers from a construction site in south China's Guangdong Province were attacked by assailants from the construction company when claiming their unpaid salaries. One worker was killed.