Australia's workplace watchdog has found evidence of employee exploitation at a number of Caltex stores across the country.
Inspectors from the Fair Work Ombudsman visited 25 sites operated by 23 of the petrol station's franchisees in Brisbane, Sydney, Melbourne and Adelaide.
Just six of those stores were found to have met workplace law standards, bringing the non-compliance rate to 76 per cent.
Caltex was first put on the radar of the workplace watchdog in 2016.
Fair Work Ombudsman Natalie James said it came after the organisation received a tip-off.
"We were receiving intelligence about some practices that were of concern to us. Practices including cash payments and underpayment of workers," she told SBS.
"That is what made us decide that we need to take a very close look at what was going on in the Caltex network."
Underpayment and failure to award overtime and penalty rates were some of the breaches. But most worrying was the lack of record keeping - according to the ombudsman.
"The most concerning of the issues we found were cases where the records were deficient. When employee records are deficient we have no real way of knowing what workers are entitled to and whether they received it," Ms James said.
The investigation found most of those affected were young and migrant workers.
Sixty per cent of the nearly 200 employees the Fair Work Ombudsman obtained records for were visa holders, while a quarter was under the age of 24.
Catherine Scarf is the CEO of refugee and migrant support service AMES Australia.
She said migrants are frequently vulnerable to workplace exploitation.
"Often migrant workers, international students, backpackers, holiday makers, those kind of visas, haven't had the opportunity to understand Australia workplace culture, law," she told SBS.
"So they'll often come into a workplace straight from visa granting without that background information and may have a very different workplace, legal, structures that we're used and so may not know what to expect, what their workplace rights are.
And so that's when issues can arise."
With 1900 stores across Australia, Caltex insists only a small proportion are in breach of workplace laws.
In a statement provided to SBS, the company said it is "committed to stamping out wage underpayment" and has taken action to ensure it's not taking place.
"We are permitted by the relevant codes and under our agreements with franchisees. In mid-2016 Caltex established an audit process, an independently run whistle-blower hotline, and an assistance fund for franchisee employees who have been affected by the conduct of certain of our franchisees," A Caltex spokesman said.
Last week, Caltex announced it was moving all of its franchise stores to company operation by 2020.
The Ombudsman linked the high rates of non-compliance to the fact that most franchise operators it had investigated were from non-English speaking backgrounds.
"New arrivals to Australia, when they set up a business may not be familiar with our laws. Our laws are very complex you need to go fairwork.gov.au and make sure you understand the award rates," she said.
Ms Scarf said franchise operators also could benefit from resources in the area of workplace rights.
"I think as well as training for migrant workers in terms of understanding their rights, it would be useful to ensure franchisees have training in terms of understanding their obligations and making sure they understand Australian law and are supported by their work franchisors in terms of what that needs to be."
