The union that exposed underpayment claims by three South African chefs is stepping up investigations into the use of business visas to import cheap and exploitable labour.

The state secretary of the Construction Forestry Mining and Energy Union, Andrew Ferguson, said the union was investigating further claims of underpayment, made by workers from Korea and Lebanon in the hospitality and construction industries.

The case of the three chefs, who say they received $50 a week and were underpaid more than $100,000 each, was adjourned for three months in the NSW Industrial Magistrate's Court yesterday.

Their employer said the cash payments were part of an ample salary package and will seek a ruling from the Industrial Relations Commission that their salaries included benefits such as accommodation, medical costs and payments in South African rands.

Standing alongside the three chefs - Reevis Khumalo, 38; Elliot Dube, 32; and William Ndlovu, 38 - outside the court yesterday, Mr. Ferguson said the case highlighted the increasing abuse of business visas by employers who were importing workers to circumvent Australian labour laws.

"We found another case this week of three Lebanese concrete workers getting 40 per cent less than other workers"  he said.

"Employers are claiming skill shortages when there aren't any and getting cheap, subservient labour.  The Government refuses to address the issue.