Australia's industrial watchdog has admitted it is not investigating the alleged exploitation of foreign workers at Gina Rinehart's Roy Hill iron ore project.
The Fair Work Ombudsman says the inquiry is being spearheaded by the immigration department as the allegations relate to breaches of the 457 visa program for temporary skilled overseas workers.
The explanation hasn't washed with Labor senator Doug Cameron, a former union boss, who has accused the ombudsman of passing the buck.
"I don't think it's good enough to be honest," he told a Senate estimates hearing in Canberra today.
"There is huge potential for breaches of the (Fair Work) Act and regulations to fall through the cracks in this hand-over, pass the parcel approach that's in place."
A whistleblower at Roy Hill claims up to 200 white-collar 457 visa workers, about half of whom are Korean nationals aged under 30, are clocking up more than 84 hours a week.
The construction union asked Employment Minister Eric Abetz to launch an investigation in March, alleging the workers were being paid $16 per hour and working jobs outside those approved for their visas.
Deputy ombudsman Michael Campbell said it was appropriate the immigration department took the lead because it was responsible for overseeing the 457 program.
The ombudsman would "happily" follow up any matters if they crossed into their domain, but so far had not launched any inquiries into the Roy Hill case.
"It's not to say we're walking away from it senator," Mr Campbell said.
Senator Cameron's dissatisfaction boiled over into a heated argument with Senator Abetz, who accused him of verballing the ombudsman and misrepresenting the evidence to suit his agenda.
"He is coming here to attack the Fair Work Ombudsman irrespective of how good their explanation is," Senator Abetz said.