The two growing headaches for China's huge migrant working population are the inadequate social security and payment for working overtime, a Party congress delegate who is a lawyer said on Sunday.

A migrant worker salutes government officials after he and 76 others received a total of 2.5 million yuan ($400,000) in overdue wages, thanks to the help of labor supervisors in Chaoyang, Liaoning province, this year. LI SONGJUAN / XINHUA

A government crackdown in recent years has helped reduce cases of employers defaulting on wages, something that has plagued the 250 million farmers-turned workers, Tong Lihua, who provides legal aid to the migrant population, said on the sidelines of the 18th Party Congress.

"We handled lots of cases of migrant workers seeking overdue wages when we opened a center to help them in 2005," said Tong, director of Beijing Zhicheng Migrant Workers Legal Aid and Research Center.

But since 2007, the government has worked to protect migrant workers' rights and interests, and wage defaults have dropped significantly, he said.

The center receives 6,000 to 8,000 phone calls a year from migrant workers, and the number of consultations about wage defaults is steadily falling, he said.

But there are increasing cases nowadays of employers who do not live up to their social insurance obligations or provide insufficient overtime pay, and more migrant workers are suing to defend these rights, Tong said.

By law, employers must provide five sorts of social insurance —including work-related injury insurance — for contracted employees, and employees must be paid at least double wages for overtime.

But some employers have failed to stay apprised of their legal responsibilities, Tong said.

Tong urged the government to create more channels for migrant workers to voice their concerns and complaints and to ensure they can defend their rights.