The operator of the well-known Han's Cafe franchise in Perth short-changed foreign workers, the Fair Work Ombudsman has alleged after launching legal action.

The ombudsman claims Tram Hoang Han underpaid 100 employees at restaurants in Forrest Chase in the CBD, Subiaco, Hillarys and Midland by more than $30,000, even though she'd been warned in 2013 of the need to comply with minimum award pay rates.

Foreign workers 'underpaid' at Han's Cafe Credit:Peta Rule

The money was back paid to the workers, who included international students, 417 working holiday visa holders and 457 skilled worker visa holders.

Despite calculating the shortfall and ensuring the workers were back paid, the ombudsman is also pursuing legal action against Ms Han because she allegedly kept such poor records the agency couldn't fully quantify underpaid wages and entitlements.

The ombudsman claims Ms Han told inspectors she generally only kept time records for between two and four weeks, but they must be kept for seven years under workplace laws.

The matter is being heard in Perth's Federal Court, with a date for a directions hearing yet to be set.

- AAP