One in three backpackers and international students are paid half the legal minimum wage amid widespread "wage theft" that extends beyond fruit picking and farm work, a study shows.
A small percentage have been made to pay up-front "deposits" to secure a job in Australia or return cash to their employer after being paid, while others have had passports confiscated by employers.
The UNSW Sydney and UTS study found wage theft is endemic among international students, backpackers and other temporary migrants, a substantial number of whom experience severe underpayment.
Thirty per cent earn $12 an hour or less, about half the minimum wage for a casual employee in many of the jobs, the report released on Tuesday found.
The findings have sparked calls from unions for the federal government to stop employers exploiting backpackers and international workers.
The survey of 4322 temporary migrants from 107 countries showed:
* The worst-paid jobs are in fruit and vegetable picking and farm work, where 15 per cent earn $5 an hour or less and 31 per cent $10 per hour or less;
* Half of those working as waiters, kitchen hands and food servers are paid $15 an hour or less;
* Underpayment is also severe for those working at petrol stations or convenience stories, car washes and in retail;
* Those from Asian countries such as China, Taiwan and Vietnam had the lowest wage rates overall, while those from major English-speaking countries like the US and the UK had the highest;
* Three per cent had their passport confiscated by their employer, five per cent paid an up-front deposit for a job and four per cent had to pay cash back to their employer from wages.
The report authors said contrary to misconceptions, the overwhelming majority of international students and backpackers are aware they are being underpaid.
"However, they believe few people on their visa expect to receive the legal minimum wage," UNSW senior law lecturer Bassina Farbenblum said.
ACTU president Ged Kearney said Australia's visa system had created a pool of easily exploited labour, which employers exploit at the expense of migrant workers.
"Our broken laws not only facilitate the theft of wages, they have facilitated big businesses importing what amounts to a slave labour class of workers on temporary visas," Ms Kearney said.
"We have to change the rules and end this pattern of wage theft and abuse of labour rights."
Gerard Dwyer, national secretary of the SDA, the union representing retail, fast food and warehouse workers, called on Prime Minister Malcolm Turnbull to outline how the government would address the problem.
"It's not good enough for him to sit on his hands and allow vulnerable young workers to continue to be exploited in this way," Mr Dwyer said.
* The SDA has set up a hotline for workers who believe they could be victims of wage theft: 131 732.