A comprehensive survey of international workers and temporary migrants in Australia has found a third earned $12 an hour or less, or half the legal minimum wage.

The survey, published as a report called Wage Theft in Australia, was conducted by academics from the University of NSW and University of Technology, Sydney.

The online survey covered 4,322 respondents from 107 countries. It was open to anyone who had worked in Australia on a temporary visa and was made available in 13 languages.

The survey found large-scale wage theft was worst in fruit and vegetable-picking and farm work, where 15 per cent of workers earned $5 an hour or less. Almost a third (31 per cent) earned $10 an hour or less.

The study also found that for every 100 underpaid migrant workers, only three went to the fair work ombudsman. Of those, more than half recovered nothing.

There were several barriers to reporting wage theft. Many overseas workers were unsure of the process or believed it would be too difficult to recover the wages, and more than a quarter said they would not speak up because of fears of losing their visa.

One of the researchers, Bassina Farbenblum, a senior law lecturer at University of NSW, said the study confirmed “Australia has a large, silent underclass of underpaid migrant workers”.

“The scale of unclaimed wages is likely well over a billion dollars.”

Unions NSW secretary, Mark Morey, told The Guardian that migrant exploitation was a “national shame that Australia must confront and fix”.

This article was originally published in the NSW Nurses and Midwives’ Association publication, Lamp.