The Workplace Relations Minister, Kevin Andrews, says the Government does not directly monitor whether Australians are available for jobs now being filled by overseas guest workers.
Unions say employers are bringing in workers from Europe and Asia and paying them in their home currencies, and downgrading award conditions.
Mr Andrews says he disapproves, but says new immigration laws flagged last week should put an end to those practices.
He's told ABC TV that in several visa categories, the Government relies on Labor governments to determine whether there's a skills shortage.
"So we rely on the advice which is provided on the ground as to whether or not there is a shortage in the workforce, and whether or not it can be filled by locals," he said.