Just under half of the cheap eateries in one popular Newtown street have underpaid their staff by a collective $80,000, investigations by the Fair Work Ombudsman have revealed.

Audits of 54 cafes, restaurants and fast food outlets on King Street found just under half were underpaying their staff in some way - whether failing to pay the correct minimum wages or weekend penalty rates.

Dozens of cheap eateries on King Street, Newtown were investigated by the Fair Work Ombudsman. Credit:Christopher Pearce

A bigger group - around three-quarters of the audited businesses - were found to be non-compliant with some form of workplace law including failures to maintain records or provide staff with payslips.

The audits, conducted in November 2018, were co-ordinated to avoid the risk of 'tip-offs', the FWO said.