In one example, an employer was granted approval for 100 visas over three years, but in 18 months he had brought in 800 workers under the 457 visa. Prime Minister Tony Abbott has reopened a loophole in the 457 visa rules that will allow employers to hire unlimited foreign workers. Credit:Andrew Meares Unions say the move, which was introduced on February 14, undermines Australian job security while deliberately reopening a loophole that can easily lead to the exploitation of foreign workers. ''It is reopening a rort for employers,'' said Dave Noonan, assistant secretary of the Construction, Forestry, Mining and Energy Union. ''Even if the department checks, there is no administrative measure they can take.'' The Australian Workers Union argues it will exploit vulnerable workers. ''It's deeply concerning that in a jobs crisis, the government is sneaking through changes that undermine local jobs and conditions,'' said AWU assistant national secretary Scott McDine.

In March last year then prime minister Julia Gillard said the visa scheme was ''out of control''. During an election campaign visit to western Sydney, Ms Gillard said she wanted the 457 visa tightened ''to stop foreign workers being put at the front of the queue with Australian workers at the back''. A discussion paper in 2012 also found there was no restriction to the number of 457 workers a company could nominate once a sponsorship is approved. In the same year, mining magnate Gina Rinehart famously warned that Australians needed to work harder to compete with Africans who will work for less than $2 a day. Yet in June, the boss of Ms Rinehart's Roy Hill iron ore project, Barry Fitzgerald, backed away from using foreign workers on 457 visas, saying he was confident he could find the staff locally. Illustration: Ron Tandberg

Before the cap was introduced in 2013, the number of 457 visas was quickly rising. In the financial year 2009/10 there were 67,980 visas granted. By 2012/13 there were 126,350 visas granted, statistics from the Department of Immigration show. Unions are also known to be hostile to the visa class because it has allowed non-union foreign labour to replace unionised local workers. A spokesman for the Assistant Minister for Immigration and Border Protection, Michaelia Cash, said: ''While the Coalition is … committed to deregulation and the removal of unnecessary red tape, we are equally committed to ensuring the integrity of the 457 program.'' The changes come as the Coalition will review the overall function of the 457 visa, which unions argue is a ''stacked'' panel. ''These secretive changes come on the back of the government's announced review, which has been stacked to deliver a predetermined outcome that will hurt Australian workers,'' Mr McDine said.

Loading There are four members on the panel: John Azarias, from Deloitte Australia; Professor Peter McDonald, of the Australian National University; Katie Malyon, from Ernst & Young; and Jenny Lambert, from the Australian Chamber of Commerce and Industry. Follow us on Twitter