By Chris Hogg
BBC News, Tokyo
Over the past 17 years, thousands of foreign workers have travelled to Japan, taking part in an official scheme to learn skills they cannot pick up in their own countries.
But this year the Japanese government's own experts have admitted that in many cases trainees are used as cheap labour.
The scheme's participants want to learn from Japan's workplaces
The US state department has gone further. In its annual report on human trafficking, it said that "some migrant workers are reportedly subjected to conditions of forced labour through [its] foreign trainee programme".
Wang Jun came to Japan on the trainee scheme "because Japan is the most advanced country in Asia, and so that I can learn skills here then go back to my own country and get a good job".
Mr Wang works at a small factory in a suburb of Tokyo. He is one of four trainees in the workshop, toiling alongside 11 Japanese workers.
He sounds like he is getting the kind of experience he is supposed to on this scheme. It was set up in 1990, in order, the Japanese government says, to help poorer countries learn from Japan's mastery of the manufacturing process.
Toshikazu Funakubo, the factory owner's son, said it could be difficult to communicate with the Chinese workers. "But they are learning the Japanese culture and language. It's a very good thing for all of us."
The owner of the business, Toshiaki Funakubo, said he employed the Chinese workers because he wanted to help China. But he admitted that labour shortages in Japan were another important consideration.
"To tell the truth I want Japanese people to join my company, but at the moment we have no choice but to depend on good workers from abroad."
The problem is that widespread public aversion in Japan to the idea of immigration has contributed to a shortage of labour.
In the United States, foreign workers make up 15% of the workforce. In Japan the figure is little more than 1%.
A recent government report into its own foreign workers scheme found that, in reality, trainees are used as cheap labour and their working conditions are not properly monitored.
"The Japanese government and the ministries do not want Japan to become an immigration country," said Martin Schulz, a research fellow at the Fujitsu Research Institute in Tokyo.
"They do not want to change the cultural and social integrity of Japan, so they have a rather hands-off approach."
That hands-off approach can lead to abuses. When the government made unannounced inspections to firms employing foreign trainees last year it found that 80% of them were breaking the laws on pay and conditions.
Some of those who are treated badly on the scheme find their way to the offices of the Zentoitsu (All United) Workers Union, in the Akiharbara district of Tokyo.
One Chinese trainee said he discovered a disparity between his pay and that of other workers, but when he complained he was told that if he did not like it he could go back to China.
He did not want to give his name as he is afraid of reprisals.
"Chinese workers here do the same work as Japanese workers," he said. "The job description, the working hours are the same. But the salary and treatment are so different. I cannot understand this."
Hiroshi Nakajima, the union official helping him with his case, said a foreign worker came to ask for help almost every week.
Japan is a famously homogenous society
"Basically they have many complaints about their labour conditions. For example, non-payment and sometimes threat of dismissal, and not only these things but sometimes sexual harassment and sometimes the company keeps their passport or alien card and insurance card too," he said.
Japan International Training Co-operation Organisation (Jitco), which runs the scheme for the government, said it was aware of media reports about trainees' troubles.
But said its own research showed foreign workers were satisfied with the way they were treated.
In a statement, Jitco told the BBC that individual cases should not be used to generalise about the whole scheme.
And yet the Japanese government's own panel of experts has decided there is a need for stiffer penalties for companies that mistreat workers.
These will not be introduced for at least two years, though. It is an acknowledgement that the system is not working, but it seems there is no rush to fix it.