SHANGHAI, Aug 5 (AP) -- Chinese authorities are investigating reports that dozens of men armed with steel pipes and bars attacked a group of migrant construction workers seeking unpaid back wages, the state-run newspaper Shanghai Daily reported Friday.

It said six migrants were injured, two of them seriously, in the attack on Tuesday in Xi'an, a city in northern China's Shaanxi province. The construction firm stopped work in November after running out of funds, allegedly without paying its 150 workers a total of 800,000 yuan (US$99,000; €80,000) in back wages.

A group of workers, mostly farmers from neighboring Sichuan province, summoned local reporters to complain, and were arguing with a manager of the construction company when about 30 people arrived and began beating them, the report said.

Phone calls to the Xi'an police were not answered Friday morning.

The newspaper highlighted the attack as a sign that labor laws meant to protect migrant workers. Official reports put the number of such itinerant laborers at 140 million, most of them underemployed farmers who seek construction work and other manual labor disdained by city dwellers.

Top communist party leaders have been demanding better enforcement of laws meant to protect such workers, but implementation at the local level is weak.

"Migrants deserve respect," said an editorial page headline. It said the case was "but one little sliver of a nationwide story. Migrant workers often work extremely long hours, receive little pay and routinely are forced to wait a long time before collecting wages."

It said Shaanxi province as a whole owed migrant workers an estimated 1.4 billion yuan (US$171 million; €140 million) in unpaid wages. Nationwide, such workers were owed some 100 billion yuan (US$1.2 billion; €1 billion) as of November last year.