The '457 visa scheme' is the Orwellian-sounding term given to Australia's programme for temporary guest workers. Last year nearly 40,000 of them - including just over 2,000 from mainland China - came to Australia to help alleviate the country's chronic skills shortage. Life has been surprisingly tough for some of these mainlanders. Just ask 38 of them employed in Sydney by a company called Hunan Industrial Equipment, which makes factory parts for a tissue manufacturer in Australia. It turns out that the firm has been underpaying the workers by between A$15,000 (HK$90,290) and A$30,000. Last week it was ordered to make up the shortfall by paying them a total of A$650,000, by the Office of Workplace Services, the Australian government's workplace regulator. That was not an isolated case. Melbourne printing firm Aprint was charged with underpaying four Chinese workers hired under the 457 visa scheme. Aprint owed them A$94,000 for unpaid overtime and weekend work. The agents in China who find potential workers for Australian companies are also exploiting the 457 visa system. Take the case of Fu Zhihong, a printer, who was brought to Australia on a 457 visa last year. Parliament was told last week that Mr Fu had to pay his agent, the Shanghai Overseas Employment Service, the exorbitant sum of A$21,000 - and buy his own plane ticket - so he could take up employment in Australia. The employment service also made him sign a contract banning him from getting anyone pregnant while working in Australia, seeking new employment, joining a trade union or being involved in political activity. Under Australian law, such contract terms are illegal. Now Mr Fu has been sacked by his employer in Melbourne because he broke both his wrists at work. Under his contract, the employment agency was supposed to help him in situations like this. But the agency hasn't returned his calls. The Department of Immigration says he could be deported for being out of work for 28 days while he was recovering. Immigration Minister Senator Amanda Vanstone has written to her Chinese counterpart about his case. But it's hard to see what she can do: her own departmental officials said last week that Australia was effectively powerless to stop the unscrupulous practices of such employment agents. The Australian trade union movement has been quick to jump on these cases of exploitation. Many unions are campaigning to have the 457 visa system abolished. The Labor Party wants the programme reformed, to ban overseas agents from employing people to work in Australia. The recent abuses of the visa system have given unionists an opportunity to warn Chinese workers who might be thinking of coming to Australia to work on a short-term basis. A union representative took that message directly to Beijing last month, to meet with the All China Federation of Trade Unions. Steve Walsh, an official from the Australian Manufacturing Workers Union, had a blunt message for Chinese workers: if you come to Australia under the 457 visa system, you could end up being exploited by employers. But, for desperate employers in Australia, China provides a welcome source of skilled workers. Darren Thomas, who runs an abattoir in South Australia, has employed over 100 mainland workers under the visa system. Mr Thomas, whose company has grown from 240 workers six years ago to over 1,000 today, says he cannot find enough Australian workers to fill jobs. There is no way that Australia can, or should, close off avenues of employment to mainland workers. But it needs to ensure that they are treated with respect and dignity. So far, that has not always been the case. Greg Barns is a political commentator in Australia and a former Australian government adviser