When he disagreed over the salary with the subcontractor who delayed signing of the contract, Mr Zhang and his fellow workers did not suspect they would not be paid and completed the six-month job.

Mr Zhang has paid a heavy price for his naive optimism, like many construction workers - especially those without a contract - because the subcontractor paid only a portion of the wages during the early stages of the job.

When the work was completed in September, the subcontractor owed 61 workers from his Henan team a total of 128,000 yuan in wages, Mr Zhang said.

Their fight for back pay has not been made any easier or cheaper, despite the government's recognition of the problem.

Mr Zhang said he first went to the labour and social security bureau in Beijing's Haidian district, but officials told them they could be of little help because they did not have the power to enforce the law.

'They told me all they could do was to talk to the subcontractor, but they did not have the power to order the subcontractor to pay,' Mr Zhang said.

'They asked us to go to the court to sue the subcontractor and said that was the fastest way.'

Despite several years of government efforts to clamp down on wage arrears and an intense propaganda barrage about its successes in recovering money owed to workers, back pay remains a serious problem on the mainland despite a degree of improvement.

A Xinhua report last Wednesday said a total of 1.63 billion yuan in wages was owed to migrant workers in Beijing.

If each worker was owed an average of 2,000 yuan in back pay, that would mean that more than 800,000 migrant workers in Beijing are owed wages by their employers. A People's Daily report last Tuesday quoted a survey by the Ministry of Labour and Social Security saying that only 65.7 per cent of migrant workers signed contracts with their employers and back pay was still an issue.

While the survey did not show the extent of the problem, it said employers usually owed workers who did not receive all their wages an average of 2,100 yuan each.

Although some governments have issued regulations to punish workers who try to get their wages through 'malicious means', desperate workers still resort to radical action, including threatening to jump from buildings or laying siege to their employers' offices.

One ironic example was a protest last week by construction workers outside the office of Farmers' Daily - a newspaper known as an advocate of farmers' welfare. More than 60 migrant workers staged a sit-in demanding 400,000 yuan of overdue payments. As in many other back-pay cases, the newspaper said it had paid the developers for work on its offices, but somehow the subcontractors had failed to pay the workers.

Li Tao , chief co-ordinator for Facilitators, a non-government organisation that helps migrant workers, said that although the problem had eased a little, the reasons behind it had not changed.

He said the root cause of the rampant back-pay problem in the construction industry was the multi-level system of subcontractors. Back pay would remain a problem without structural change in the industry, he said.

Some workers still had to resort to extreme methods because the cost of fighting for overdue wages remained too high, and the government's publicity campaign to protect migrant workers had failed to deter dishonest employers from ripping off migrant workers.

'Even if an employer loses in a lawsuit, what does he lose?' Mr Li asked. 'He will just have to pay the back pay to the workers and he is supposed to pay that anyway.'

It was the workers who had to compromise with their employers and forgo a portion of their wages because the cost of demanding back pay was too high, he said.

'Employers may threaten workers that it will take a long time if they file a lawsuit and they should take, say 60 per cent of the wages and leave,' he said.

Mr Li said the government should impose penalties on employers who lost back-pay lawsuits, to stop the problem.

And even when migrant workers won a lawsuit, courts were often unable to carry out the ruling because the subcontractors might have absconded.

Although the government had ordered subcontractors to pay workers on a monthly basis, it rarely happened in reality, Mr Li said.

After four months, Mr Zhang has finally managed to get legal aid, but there has been no word on whether the court will accept his case.

'It is so difficult for migrant workers to demand back pay,' he said. 'We go to find a lingdao [official in charge] and they don't care. The government said the money should be paid to workers every month, but we don't even have a cent.'

Like many other team leaders who have failed to pay the workers they recruited, Mr Zhang said he had to brace for a stressful Lunar New Year because the workers he had recruited would ask him about their salaries when he went home for the holiday.