The Fair Work Ombudsman's 2019/20 annual report shows the amount recovered is more than three times that of the previous financial year.

Major employers dobbing themselves in represented a significant chunk of underpayments, with large corporations increasingly self-reporting since July 2019.

Those matters typically involved large and complex underpayments affecting thousands of workers over several years.

"The prevalence and the scale of this type of non-compliance is extremely disappointing and concerning," ombudsman Sandra Parker wrote in the report.

She said FWO's compliance and enforcement work, along with negative community attitudes to ripping off workers, was acting as a deterrent.

More than $56 million was recovered through enforceable undertakings, while $7.8 million was paid back due to almost 1000 compliance notices.

Fast food outlets, restaurants and cafes accounted for 50 per cent of legal action the ombudsman initiated over the financial year.

Australian Associated Press