The Fair Work Ombudsman recovered the money for 17,718 workers in 2018/19, according to the organisation's annual report released on Monday.

The workplace watchdog confirmed fast food restaurants and cafes are a key priority, with a series of high-profile wage theft scandals plaguing the industry in recent years.

Hospitality accounted for 36 per cent of all reports, almost tripling the second-ranked sector, which was retail.

Three sushi outlets in regional NSW underpaid 31 employees - including young people and visa holders - more than $70,000, resulting in $383,616 worth of penalties.

Some 54 workers were underpaid $73,347 at a cafe leading to a $257,000 fine.

A Brisbane-based wireless technology and radio communication business was slapped with a record penalty of $105,000 for failing to comply with an unfair dismissal order.

A Sydney fashion start-up and its director were penalised almost $330,000 for underpaying three workers more than $40,000.

One of the employees was a graphic designer with a university degree who worked two days a week for nearly six months without pay before getting just $1000.

In another case, an online news service covering regional Queensland and its director copped a $264,924 penalty for underpaying young journalists and production staff.

The company also had to back-pay 23 workers more than $300,000 in underpayments.

A company running a 7-Eleven franchise and a Japanese restaurant in Melbourne was penalised $335,664 for underpaying Chinese workers.

Three international students working at the 7-Eleven were made to repay their wages as part of an illegal cashback scheme.

Upwards of $1 million was recovered for more than 2500 workers as part of a targeted blitz on horticultural businesses.

The FWO report noted an increasing intolerance for underpayments to workers.

"A changing workplace environment increases the opportunity for unscrupulous employers to evade detection, particularly where vulnerable workers are employed," ombusdman Sandra Parker wrote.

"Wage exploitation of migrant workers also remains a complex issue as it crosses employment, migration, corporations, taxation and other laws."

Australian Associated Press