Woolworths has been heavily criticised by the Fair Work Ombudsman over the underpayment of trolley collectors working at its supermarket stores.

In a new report, the ombudsman said it uncovered workers employed through trolley collection service providers who were being paid as little as $10 per hour.

"These are workers who are entitled to between $18 and $22.50 per hour," Fair Work Ombudsman Natalie James said.

The ombudsman said it inspected 130 Woolworths sites across the country.

Woolworths responded by saying it had improved its practices since 2014, when the research was carried out.

Almost 49 per cent of those sites presented reports of underpayment or a lack of timekeeping record, and payslips.

Some form of non-compliance with workplace laws was found at 79 per cent of sites, the report said, adding that many of the trolley collectors were overseas workers.

Ms James told the ABC Woolworths needed to have better oversight over its agreements.

"There were cases where there were many, many layers of contracting. Woolworths' own rules said there were only meant to be two levels of contracting," she said.

The ombudsman's report concluded that Woolworths had a business strategy seeking to transfer its capital risk, and was now calling on the chain to take responsibility for underpaid workers.

She said action is being taken against the service providers who are directly responsible, but Woolworths still had an obligation to ensure workers were not being exploited on its supermarket sites.

"Of course the contractors who employ these workers are directly responsible, directly liable. But the question we are putting to Woolworths is 'what contribution has their lack of oversight in the supply chain had in bringing this about?'"

Woolworths has measures 'to ensure compliance'

In a statement, Woolworths said it actively cooperated with the ombudsman and would continue to do so.

It said the report contained issues not presented to the company, and it could therefore not respond.

"Woolworths believes that if the FWO were to conduct an inquiry into trolley collection procurement practices as they exist today, our arrangements would not be open to criticisms of the kind levelled in the FWO's report," the statement read.

It also said it had implemented measures since 2014 to "help ensure compliance" by contractors.

These included mandatory independent audits and educating contractors.