THE company behind what may be one of the largest immigration rackets ever reported in Australia is still in business four months after it was investigated because the Department of Immigration is not certain it has sufficient evidence to prosecute.

The Workplace Ombudsman is unable to warn potential migrants of the allegations against the labour hire firm.

The department alleges that an unnamed company – which the Sydney Morning Herald named as Regional Labour Supply – was involved in the production of false work documents and had supplied illegal labour along the east coast.

It is also alleged by a former manager of the company and a former union official that workers sourced through the company were underpaid, stripped of their passports, kept in houses with as many as 16 people and sent to work with false documents.

‘‘You’re looking at going back 100 years in the way they were getting treated,’’ the former Queensland secretary of the Australasian Meat Industry Employees Union, Russell Carr, said of the workers. ‘‘It was like something you would read about out of the Third World.’’

On March 11 the department raided meatworks across three states. As many as 100 people were thought to be working on false or invalid visas – 82 were located, 45 were placed in immigration detention and eight left the country. Offices were raided and fake passports seized.

The department is investigating one man in relation to the racket. Officials would not name him, but the Herald understands he is Scott Shi, the former director of the Auburn-based Regional Labour Supply. Despite evidence from the raids, no action has been taken against Mr Shi or Regional Labour Supply.

‘‘We are confident we’ve significantly disrupted the operations of the identified labour-hire intermediaries who are the subject of a major ongoing investigation,’’ a spokesman for the Department of Immigration said. ‘‘It’s not our job to shut down these operations … it is still under investigation but we have been in liaison with the Commonwealth Director of Public Prosecutions to gauge if, in their opinion, we have enough evidence to press charges.’’

A former manager at the company’s Biloela office, who refused to give his name, said workers – many of them on tourist or student visas – had their passports taken when they joined the company. He said the original passports were kept in Sydney and the workers were supplied with photocopies.

In the time he worked for Mr Shi he did not see a single visa or work permit. ‘‘That’s not my concern. My job was just getting them work,’’ he said. ‘‘After a few months they ask for actual passports. I was told the passports were kept in Sydney.’’

The former manager said he rented three house for the 30 people he managed. As many as 16 were kept in one house, he said. The Herald understands the Department of Immigration began its investigation after a complaint from the Australasian Meat Industry Employees Union.

Mr Carr, who was the Queensland branch secretary in the months before the raids, said he had received letters from migrant workers made to pay $200 for the Q-fever vaccinations required to work in an abattoir.

In another instance, all workers had their pay docked by $20 when a tyre burst on the bus used to ferry them between work and their crowded homes.

The migrants were paid a fraction of the wages given to Regional Labour Supply by the meatworks, Mr Carr said, and were not told how much tax they contributed.

‘‘He wasn’t giving them pay slips. He was informing them by mobile when they got paid,’’ Mr Carr said. ‘‘They didn’t pay correct tax or super. They didn’t know what tax they were paying.’’

Mr Shi declined the Herald’s invitations to interview him.