Vulnerable foreign workers are being paid far below national standards in a jobs "black market", according to a union investigation.
A two-year audit of local job advertisements on Chinese, Korean and Spanish websites, released by Unions NSW on Monday, found almost 80 per cent of proposed rates were under the minimum award wage.
Union secretary Mark Morey says the audit found a total underpayment of $1.62 million across 200 job advertisements - which amounted to $8000 per business over the course of a year.
"The figures themselves are far in excess of what we thought the problem was," Mr Morey told AAP.
"There is a business model in Australia where people think they can pay community rates rather than the legal rates in this country and it's a real problem across the board."
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Mr Morey said foreign workers were often scared to speak out about being paid too little.
"Some people are just fearful of coming forward to complain about employers for the ramifications that may occur from that, such as having their visa cancelled," he said.
The union gave examples of a Korean woman, Angela, who arrived in Australia four years ago and worked picking blueberries for about $6 an hour near Coffs Harbour.
Meanwhile, a man from Hong Kong was paid $5 under the award wage in a Brisbane warehouse driving forklifts.
Unions NSW is demanding greater powers under the Fair Work Act to inspect businesses' wage books if they're suspected of ripping off workers.
"We think there should be some powers given back to unions to be able to inspect wage books where they can demonstrate there is systematic wage theft going on," Mr Morey said.
The worst industries for underpayment were hospitality and cleaning, according to the union.
A spokesman for Federal Employment Minister Michaelia Cash said the government didn't tolerate exploitation of workers.
"This is why the government has introduced the vulnerable workers legislation into parliament to protect workers and impose heavy penalties on employers who deliberately and systematically underpay them," he told AAP in a statement.
As for allowing unions greater powers to investigate underpayment, the spokesman said the Productivity Commission inquiry did not recommend changes to union entry.
