The inquiry follows an examination of the issue by Fair Work Ombudsman Sandra Parker who found in a Tasmanian investigation evidence of underpayments of more than $64,000.

The inquiry focused on 55 supermarket sites, including 31 Woolworths, 17 IGA and seven Coles stores but eventually focused on Woolworths’ cleaning labour supply chain. 

The subsequent report found the chain’s procurement process and oversight of contracts had contributed to a “culture of non-compliance”.

This included significant underpayment of cleaners, breaches of subcontracting terms, and corporate structures reliant on procurement of vulnerable workers.

Drawing on 2016 Census data, Ms Parker said 50 per cent of cleaners in Australia were born overseas, 40 per cent spoke another language at home besides English, and 28 per cent did not have an Australian citizenship.

She said her office had so far recovered $21,332.37 in underpayments.

Ms Parker said the remainder of the money was outstanding because an employer had either left the jurisdiction or the affected employee had been unable to provide evidence of underpayment.

Woolworths general manager of facilities management, Trent Mason, said the business had a cleaning network of 16 head contractors, 425 sub-contractors, and 3000 cleaners.

“We have worked with our contractors to ensure individuals have been paid their entitlements, and on corrective actions to ensure the causes of non-compliance are rectified to prevent recurrence,” he said. 

“No audits have identified evidence of deliberate underpayment or exploitation of workers.”

Coles, Tasmanian Independent Retailers and Master Grocers Australia will also be represented at the hearing in Devonport on Wednesday, as will United Voice.

Union lead researcher Frances Flanagan said the Fair Work Ombudsman’s investigation found non-compliance with the Cleaning Services Award at 90 per cent of Woolworths sites. 

“The nature of contract cleaners as a highly dispersed and hidden workforce means that the true extent of exploitation cannot be determined with precision,” she said.

The Senate committee is due to report in October.