Some building industry employers are more than willing to take on undocumented immigrants because they're seen as cheap and hassle free labour, according to one leading engineering academic.
Auckland University of Technology's built environment department professor John Tookey said a shortage of willing local workers combined with the costs of employing local tradesmen were partly to blame for an increase in undocumented immigrants getting construction work in New Zealand.
Nearly 200 illegal workers from Malaysia were deported or stopped at the border last year following a six month immigration investigation.
Professor Tookey said it was no surprise that construction firms were willing to employ illegal immigrants, as they would work for longer for less.
"You've got somebody who's willing to go anywhere, anytime to work as long as it requires to get the job done.
"And all that they want to do is get cash in hand and walk away," he said.
"You have minimal liabilities thereafter, you don't have to do crazy little stuff like KiwiSaver or any of that sort of stuff.
"It's something which a lot of companies are more than willing to accept."
Operation Spectrum, which began in May last year, found the construction workers getting paid between $20 and $40 an hour cash - and none had paid tax.
The Registered Master Builders Association said it wanted to work with the government to help put a stop to undocumented immigrants working in the industry.
Master Builders chief executive David Kelly said the availability of cheap labourers who did not pay tax was not fair on people legitimately looking for work.
"People not paying tax [is] undermining legitimate businesses and workers from filling those jobs," he said.
He also voiced concern for the immigrant workers themselves.
"I think when people take advantage of this and exploit workers, they're very vulnerable and so that's another reason why we would want to see it stamped out as soon as possible."
He said undocumented immigrants did not have the legal protections granted to other workers.