In the past financial year the Australian Building and Construction Commission recovered $823,724 for 1376 workers.

The total recovered since the ABCC was reinstated in December 2016 has been more than $1 million.

Labor senator Tony Sheldon said on Wednesday industry bodies estimate $6 billion in unpaid wages across the sector.

"There are many billions of dollars being stolen in this industry in the form of wage theft," he told a Senate estimates hearing in Canberra.

He suggested ABCC commissioner Stephen McBurney talk to government departments, consult employer associations and read newspapers to learn the extent of the issue.

"You're telling me $1 million is a good job, well done?" Senator Sheldon asked

But the commissioner doesn't regard it as a low figure.

"That's a significant amount for the individual employees who had been subject to the underpayments," Mr McBurney said.

He said the vast majority of wages recovered were as a result of proactive audits, with workers and unions rarely bringing complaints to the agency.

During 2018/19, courts whacked the construction union with $4.2 million in fines due to Australian Building and Construction Commission proceedings.

In the same period three employers were fined more than $36,000.

Mr McBurney said he would welcome the CFMMEU referring underpayment allegations, insisting the agency was there to represent all building industry participants.

"If the union was minded to refer matters of underpayment of workers to my agency, you can rest assured I will take all necessary action under my Act," he said.

Australian Associated Press