Korean, Chinese and Spanish-speaking workers are routinely paid below minimum wage as part of a "seedy underbelly of wage theft", a report from Unions NSW claims.
An audit of 200 job ads, conducted in 2016 and 2017, on Korean-language website Hojunara, Chinese website Sydney Today and a number of Spanish-language Facebook pages, found nearly four out of five (78 per cent) advertising below the minimum award wage.
They included a serving and kitchen aid at a Korean restaurant in Strathfield in the city's inner west paying $13 an hour, a position advertised in Chinese for warehouse work in the western suburb of Smithfield paying $16 an hour, and a position advertised in Spanish for a cleaner paying $15 to $20 an hour.
"This is wage theft on a massive scale. And it's being perpetrated against people ill-equipped to fight back," Unions NSW Secretary Mark Morey said in a statement.
"Migrants often know they are being ripped off but lack the language skills, confidence and support to stand up for their rights. Often migrant workers are threatened, or must consider how a complaint will affect their visa or residency status."
According to the report, 100 per cent of jobs advertised in Mandarin and Cantonese were below award rates.
Hospitality was the worst offender, with the average rate of pay advertised at $13.60 an hour, compared with the award rate of $18.29 an hour.
Based on the advertised rates for the 200 jobs audited, the total annual underpayment would equate to $1.62 million.
Unions NSW says it will use the report findings to push for greater right of entry powers at the upcoming NSW Labor conference.
"We intend to keep shining a bright light on this problem while taking action against wage theft employers," Morey said.
"Our research finds that some employers believe they can offer a 'Korean', 'Chinese' or 'Spanish' rate of pay. Your pay rate is not determined by passport or ethnicity. We are all entitled to Australian standards.
"Allowing unions better access to dodgy workplaces would empower workers to stand up for their rights as would criminal sanctions against wage thieves. These are both measures that should be adopted by Commonwealth and NSW governments."
Unions NSW has created an online register of businesses which it claims are aware of their obligations and "continue to systematically underpay workers".
The Fair Work Ombudsman has been contacted for comment.