The Fair Work Ombudsman has made surprise visits to restaurants, cafes and fast food outlets in Darwin.

Around 50 businesses in various suburbs including Darwin City, Casuarina and Palmerston City were targeted.

The Fair Work Ombudsman worked with multiple sources who reported tipoffs regarding underpayments.

Selected businesses were assessed based on centralised postcodes for signs of non-compliance, with the Fair Work Ombudsman honing in on food outlets sponsoring visa holders.

The surprise visits are part of a national initiative that has already targeted eateries in Melbourne, Brisbane, Sydney, Adelaide, Perth, Hobart and the Gold Coast.

More than $500,000 in unpaid wages has been recovered for 555 workers across Melbourne and Brisbane so far.

The Ombudsman issues a strict warning to businesses breaching workplace place laws and can apply a court ordered penalty of up to $33,300 for non-compliance.

Individuals can face penalties up to $6,660 for a compliance notice breach and up to $13,320 for a record-keeping breach.

Image credit: Northern Territory