By Louisa Lim BBC in Beijing

One such worker battling to get his wages is Gao Mingyu.

His khaki cotton jacket and cloth shoes seem too thin to protect him from the chill of the Beijing winter.

I would sacrifice my life to get that money back Gao Mingyu Migrant worker

He does not flinch from the cold, though his lined face tells a tale of suffering.

His plight is magnified at this time of year, as tens of millions of other migrant workers head home to enjoy Spring Festival with their families.

Gao Mingyu used to till the fields in central Henan province.

But lured by the promise of riches in China's cities, he came to Beijing two years ago, bringing around 50 young men from his home town with him.

For three months, they worked on a building site for a large state-owned company, Shougang Corporation, which is also known as Capital Iron and Steelworks.

But Mr Gao says they have still not been paid.

"Every day they made us work 12 hours because the work schedule was so tight," he says.

"I did everything - digging, carpentry and painting. Of course it was tiring. But we did it because we're peasants and we wanted to earn money. But until now, we haven't been paid anything. "

Political Issue

Since then, he has been trying to get back the unpaid wages owed to him and the other workers - a sum of more than $15,000 in total.

It is a familiar story, and one which has become a political issue for the Chinese leadership.

Gao's team came from his home town

Late last year, Premier Wen Jiabao was asked for help by a woman whose husband had not been paid for working on a government-financed construction project.

He ensured that the money was handed over.

But the scale of the problem is still unclear; statistics from the All China Federation of Trade Unions say rural labourers are owed about $12bn, but some estimates put that figure as high as $40bn.

Premier Wen has now ordered companies to clear the back pay owed to workers, but the reality is rarely that simple.

Help for workers

In Mr Gao's case, he and the other workers took the job without signing a contract.

Now they have no legal proof of their claim. He has tried many official avenues, but with few results.

"I've been to the courts, to the Beijing city labour ministry and to the municipal work inspection team," he says.

"At first they said they could help me, but they didn't do anything."

In desperation, Mr Gao turned to a Beijing-based non-profit organisation helping migrant workers, Xiaoxiao Niao.

This was started by a former migrant worker, Wei Wei, who accompanies Mr Gao to an office of the Shougang corporation for negotiations.

As they walk towards the company's office, Wei Wei sets out their aims.

"We hope the company can see that migrant workers aren't powerless, that we are helping the migrant workers and the media is concerned about their plight. Companies shouldn't discriminate against migrant workers."

But once inside, it does not take long for the looming confrontation to explode.

Many of the problems faced by workers involve sub-contractors

"I worked for you sometimes for 14 hours a day," Mr Gao shouts, "Why won't you pay me?"

"I don't even need to see you," the company representative replies. "We've already paid the sub-contractor."

Stranded

It is a complicated and depressing story. The company says it has paid an independent middleman for most of the work, who has produced receipts from the workers vouching that they have been paid.

As Mr Gao leaves the office, there is little to raise the hopes of his workmates, who are waiting for him outside. These are the young men who he brought to Beijing.

They are all stranded in the capital, and as team leader, Mr Gao feels responsible for their fate.

"We have got no money at all," one of them says. "Not a cent."

For Gao Mingyu, there are few options left. Last year he borrowed $2,000 for his daughter's education, and the interest on that is increasing all the time.

He has not seen her since he first left home to find work in the capital.

And when he thinks about his 70-year-old mother waiting for him at home, he breaks down.

"I would sacrifice my life to get that money back," he sobs.

His story is all too familiar - it's estimated millions of others are in the same position.

And it is tales like this that breed resentment against China's leaders who - despite issuing orders - seem powerless to improve life for the victims of the country's economic boom.