In Australia, the national minimum wage is 18.29 Australian dollars, or $13.84, per hour. Casual employees, who are not entitled to vacation or sick leave, typically make more.

The worst paid jobs were in fruit and vegetable picking and farm work, according to the survey.

“We know now that this is entrenched, it’s widespread, and for many of these migrant workers, wage theft is severe,” said Bassina Farbenblum, a co-author of the report and a lecturer in law at the University of New South Wales in Sydney.

Many of the workers knew they were being underpaid, the survey found. Because of their visa status, the authors said, they probably did not expect to receive the legal minimum wage.

“We’ve got an invisible, large, low-wage labor market,” said Laurie Berg, a law lecturer at the University of Technology Sydney and a co-author. “The issues are disguised and we’re not addressing that.”

The authors, who worked with local migrant and worker groups, acknowledged flaws in the survey, which included about 4,300 workers and was translated into 12 languages other than English. It was conducted online, which could exclude some groups, and because it was anonymous it could be completed more than once. Participants were invited to apply for a drawing for a total of about $1,000 in Amazon gift cards.

Still, its conclusions roughly match those of some Australian government officials. Young people and people from migrant backgrounds may be more susceptible to exploitation in the workplace, said Mark Lee, a spokesman from the Fair Work Ombudsman, an independent government agency that investigates workplace complaints and enforces labor law.

He added that this was because of a variety of factors, including “language barriers, lack of understanding of their workplace rights, limited knowledge of where to go for help and concerns over their visa status.”