Inland Revenue has launched a new advertising campaign warning tradespeople that cash jobs can be traced.

IRD, which uncovered $159m of unpaid tax from the cash jobs and the "hidden economy" last year, said that the message will appear online and around Auckland, Wellington and Christchurch in bus shelter ads and other outdoor advertising.

Inland Revenue marketing and communications group manager Andrew Stott said a big proportion of cash jobs were in trades like plumbing, building and electrical work.

"There's a misconception out there that this work flies under Inland Revenue's radar but undeclared income leaves a trail, which can be easily uncovered when looking for irregularities in a tradie's books."

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"You place yourself in a difficult position when you accept these jobs so the best advice is to record everything, declare every dollar and make sure you're charging GST if required," he said.

IRD said that about 25 per cent of people were prepared to pay a tradie with cash, compared to 35 per cent six years ago.