The rort goes like this. A cleaning firm wins a contract to clean a big office building. Its tender allows for wages of about $25 an hour for the cleaners. The firm then hires “subcontractors” to do the cleaning and pays them something much less, say $15 an hour. The margin leaves room to undercut the competition and pocket the balance.

At $15 an hour, the cleaner is missing out on more than $15,000 annually. This is not a hypothetical or a once off – it’s the reality in at least a quarter of the big buildings in Melbourne’s CBD, according to the union representing these workers.

United Voice has released a report, A Dirty Business, which is based on a seven month covert investigation into practices in the industry. It found that more than half of the cleaners working in Melbourne’s CBD are international students.

These students pay extortionate fees to attend Australian universities. Annually, fees and living expenses average $38,000. Student visa holders are ineligible for concession cards and are subject to strict work restrictions. Often, they work to make ends meet under threat of deportation.

Breaking their visa conditions, or having a boss who will say they did, can give employers control over an international student’s right to remain in the country. If student workers make a fuss at work or annoy the boss, they can easily be dobbed in to Immigration.

The work they can get is characterised by insecurity. Workers report that jobs come by texting your name to a given mobile number, and they can be terminated as easily.

Bullying is rampant. Sarita, interviewed as part of the report, said, “From the first day I was not happy. There was a supervisor who used vulgar words. I didn’t like that and there was harassment. He would say things like, ‘You fucking girl – clean it up properly, otherwise I sack you.’”

Pay is irregular. “[The pay] was always a week late and the workers had to chase up with the agency to find out why, when they are going to get paid, when the money is going to get deposited and they just kept saying – it’s going to come.”

Union access is made difficult. Under right of entry laws, unions have to give 24 hours’ notice before entering a business to speak with workers. In the cleaning industry, often by the time United Voice can get in, all of the “subcontractors” are “out sick”. The union was shown text messages directing cleaners not to talk or to say that they worked for the main firm.

These tactics haven’t stopped the union getting to these workers though. A Dirty Business is released as part of the Clean Start campaign, which has had successes in organising workers and lifting conditions across the industry.

A former “subcontractor” who has won a better deal argues, “It is a lot better … [we] get paid on time and also … regular meetings and information about Work Safe.”