A South Australian fresh produce trader has avoided legal action, despite being found to have underpaid an Indonesian worker by more than $US42,000 over nine years.

The Indonesian man, who worked for the trader at a market in the South Australian capital, Adelaide, recently complained of his underpayment to the Workplace Ombudsman and was then threatened with dismissal.

The company has escaped court action but has been ordered to pay back the money.

Ombudsman spokesman Craig Bildstein says some employers take advantage of migrant workers.

"People from non-English speaking backgrounds are vulnerable workers, just like young people are vulnerable workers and for us they are a priority. Any worker has workplace rights and it's our role to enforce them," he said.