Thousands of tradesmen right across the country are on notice.

The tax man is on to you.

They've allegedly been been quoting hardware giant Bunnings' Australian Business Number on their invoices in a wide ranging scam that undermines the tax system.

It's raised serious questions about the ABN system which has been running for 17 years now.

Abuse is particularly rife in some parts of the country more than others. In the Northern Territory about 40% of all invoices have ABNs for Bunnings.

The rampant practice is making it near on impossible to trace where the money is really going.

There's nothing to suggest Bunnings has done anything wrong besides being the hardware store of choice for the country's tradesmen.

It's prompted a push for a review of the ABN regime which was brought in with the introduction of the GST.

It's believed 3.5 million ABNS have never lodged a tax statement or tax return.

A taskforce investigating the 'black economy' will deliver its final findings around October.