Almost 50 workers at United Petroleum petrol stations have been underpaid more than $20,000, collectively, because of incorrect hourly rates including penalties, the Fair Work Ombudsman says.
An ombudsman audit of 12 outlets beginning in 2015 found that 19 workers were in total underpaid $12,105.09.
These outlets were owned by franchisees or commission agents and one was staffed by Keycomp, a business associated with United Petroleum.
Another audit of all Keycomp console operators, conducted by United Petroleum at the ombudsman's request, found an additional 27 employees were owed a total of $8,445.74.
The ombudsman said all 46 cases involved the payment of flat rates for all hours worked and the incorrect application of penalty rates.
Many underpaid workers, franchisees and commission agents involved, were from non-English speaking backgrounds and had little knowledge of workplace laws or employee rights, the audit found.
It also found that United Petroleum did not have a system in place to test whether the outlets were paying employees correctly.
In one instance, a franchisee paid five casual student-visa holders an hourly rate of $18.70 when it should have been $25.05, acting ombudsman Michael Campbell said.
United Petroleum has since told the ombudsman that Keycomp no longer employs console operators at outlets.
The ombudsman said it was considering expanding its investigation into Keycomp's compliance history.
It also said United Petroleum was in discussion with it regarding systems and processes to ensure outlets' future compliance with workplace laws.
The ombudsman says it has entered into enforceable undertakings with two outlet operators, in Dee Why in Sydney and in Adelaide.