Chinese, Korean and Spanish speakers are being targeted by businesses advertising jobs paying below the minimum award wage, according to an audit of 200 job advertisements by Unions NSW.
Approximately four out of five job ads were for roles with illegal pay.
Mark Morey, Unions NSW Secretary, 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.
"This is wage theft on a massive scale. And it's being perpetrated against people ill-equipped to fight back," he said.
"Often migrant workers are threatened, or must consider how a complaint will affect their visa or residency status.”
Associate Professor Joo-Cheong Tham from Melbourne Law School, told SBS World News this was no surprise, but did highlight a "really quite remarkable gap in our labour regulation."
"If you had a job ad that was in breach of anti-discrimination job laws, that would be illegal, yes,” he said.
"But there is generally nothing illegal in advertising these wage rates that are in breach."
The job advertisements studied were randomly selected from webpages Hojunara (Korean), Sydney Today (Chinese) and a number of Facebook groups targeted at Spanish speakers from Latin America.
Eighty-seven advertisements were in Chinese, 72 in Korean and 41 in Spanish.
"Our research finds that some employers believe they can offer a 'Korean' 'Chinese' or 'Spanish' rate of pay,” Mr Morey said.
"Your pay rate is not determined by passport or ethnicity. We are all entitled to Australian standards."
The report concedes the audit provided a “relatively small sample size”, but argued it still showed “overwhelming” rates of underpayment.
The national minimum wage is currently $18.29 per hour, and a basic food and beverage attendant is entitled to $18.81 per hour.
Seventy-eight per cent of businesses studied paid below the award rate.
On average, underpaid jobs were advertised at $14.03 an hour.
Professor Tham said educating individuals about their rights and giving them better complaint pathways was important, but it would not be enough to effect meaningful change.
"The key is actually changing employer practices and that requires action on the part of the relevant statutory authority, the ATO and Fair Work Ombudsman, as well as operational health and safety agencies."
The audit found the record of businesses in the hospitality sector was particularly bad, with almost all (97 per cent) advertising below award rates of pay.
Between one in two and two in three ads in the construction, cleaning and transport industries advertised below-award pay.
Unions NSW has set up a website that is reporting businesses who have advertised rates of pay below the minimum award rate.
The group contacted 78 businesses who had advertised below the award and the ones who have not provided evidence of sufficient steps to rectify underpayment appear on the website - 21 in total.