Refrigeration and Air Conditioning Contractors Association (RACCA) president, Kevin O'Shea, has warned employers to be on the lookout for dodgy trade certificates.
Nine people have been arrested over their involvement in issuing fraudulent trade qualifications.
O'Shea said a few hundred qualifications were issued covering a range of trades such as building, electrotechnology, gas fittings, air-conditioning and refrigeration.
He said the scam begin in 2015 and the fraudulent certificates were allegedly created for buyers to circumvent completing compulsory theory and practical assessments.
Ringleaders of the scheme, Cameron Russell, 55 and wife Fay, 52, have been charged with multiple offences including falsifying documents that produced $125,000 in proceeds.
They are currently behind bars and will return to court on February 5, 2019.
According to a report in the Sydney Morning Herald, the arrests follow a long-running investigation which found the couple had been issuing fraudulent construction industry trade qualifications to unqualified people for a fee since at least 2015.
“It is estimated hundreds of fake qualifications may have been issued through the scheme, raising concerns about the potential number of unqualified people currently working on construction sites around Sydney,” the article said.