A former government inspector who investigated the building industry says threats made by CFMEU union leader John Setka to hunt down inspectors are real, suggesting they have a "better intelligence unit" than Victoria Police.

Alan, who wanted to remain anonymous, investigated strike action and breaches of the Fair Work Act for the Australian Building and Construction Commission. He said workers often cornered inspectors at construction sites, abusing them before spitting on them.

CFMEU Victorian secretary John Setka could be at risk of losing his position if the government's new laws are passed. Credit:Joe Castro

"If you got cornered on site, it happened to me once, they'd line up, and you'd try and exit the building site, they'd call it the walk of shame, they'd abuse you, try and spit on you, things like that," he told radio station 3AW on Wednesday.

His revelations come after Mr Setka threatened to hunt down and "expose" ABCC inspectors, warning: "When we come after you, you'd better be careful."