Most casual workers are not paid 25 per cent more than permanent workers in the same job, according to a new research paper released by the Australian Council of Trade Unions (ACTU).

The paper, Myth of the Casual Wage Premium, found Australia has the highest proportion of temporary labour in the OECD at one in four.

The number of workers in casual employment increased by more than half a million between 2005 and 2016, to reach 2.5 million workers. In most industries and occupations examined, the casual wage premium was five per cent or less.

According to the paper, the longer someone works in a casual position the more likely they are to be paid less than permanent staff. It also found around half of all casuals say they would prefer permanent employment with paid leave rights and job security.

ACTU secretary Sally McManus said casual pay on average is around two to five per cent more in similar occupations, and many people get paid less than permanent staff, particularly in lower-paid work – not the supposed 25 per cent premium.

“Casual work should be exactly that – work where shifts can vary and there is no legitimate expectation of ongoing work,” McManus said.

“Big business has been rorting our system, using loopholes and underhanded arrangements to pay some casuals even less than permanent workers doing the same job.”

A study released by UNSW Sydney and UTS, Theft in Silence last month found less than 10 per cent of international students and backpackers in Australia recover unpaid wages, even when they are aware they are being underpaid.

The release of the ACTU’s Myth of the Casual Wage Premium paper also follows calls by the union last week to appoint an anti-slavery commissioner in order to clamp down on corrupt and illegal business practices.

More than 40 million people worldwide are believed to be victims of modern slavery, including 4300 Australians.