''When we see evidence that something is not right with the program - such as spikes in particular sectors that are out of step with growth in those industries - we must take action to stamp out any rorts,'' Mr O'Connor said.

For the first time, Mr O'Connor sought to quantify his argument that the system was prone to rorting, saying more than 10,000 people were abusing the scheme.

''Insofar as numbers, I believe that the areas where there's been an illegitimate use of 457s numbers [is] not negligible,'' he said. ''I would say it would exceed over 10,000.''

This is about 10 per cent of the 105,600 457 visa holders in Australia. The Minister's office could not say where his figure about the number of people rorting the system came from.

Mr O'Connor said he would introduce legislation to close loopholes in the scheme when Parliament resumes in May.