Rebuild tradies are disputing claims that Christchurch is one of the worst areas for tax crime.

A new Inland Revenue campaign's heading to Auckland, Wellington and Christchurch to combat cash jobs.

IRD says the rebuild makes Canterbury ripe for untaxed work, with some cash jobs worth up to $20,000.

That's disputed by the Christchurch-based manager of tradies network Builderscrack.co.nz .

Jeremy Wyn-Harris says he's never heard of $20,000 jobs, but says cashies are very hard to police.

"I don't think it's possible to eradicate it.

"I think people need to use their judgement, it's up to individuals a lot of the time to make sure that they don't do cash jobs, whether that's a homeowner or a tradesperson."