Australian retail giant 7-Eleven has been found to be systematically paying its workers about half the minimum wage at stores around the country.

Key points: 7-Eleven employees worked twice as long at half the pay

7-Eleven employees worked twice as long at half the pay Investigation found three out of five stores underpaying staff

Investigation found three out of five stores underpaying staff Overseas students systematically underpaid, threatened with losing visa

A joint Four Corners and Fairfax investigation has uncovered evidence of collusion between some of the owners at hundreds of stores across multiple states.

Former employees have told of being made to work twice as long as expected at half the rate of pay, with some earning as little as $10 an hour.

Internal company documents show that as recently as August this year, 7-Eleven reviewed the payroll at 225 stores and found 69 per cent had ongoing payroll issues.

It is the first in a series of reports that will expose the breadth of wage fraud within the massive network of stores.

Documents show franchisees are continuing to ignore the law and underpay staff, even after being brought before the courts.

The Fair Work Ombudsman recently launched an investigation into the wage fraud across 7-Eleven stores — the third such investigation in six years.

In September 2014, the Fair Work Ombudsman raided 20 stores in Melbourne, Sydney and Brisbane and found three out of five stores were underpaying staff.

The office is expected to release a report later this year.

Half pay scam exposed

7-Eleven has come under particular fire for its treatment of overseas students.

Consumer advocate Michael Fraser started asking questions about staff pay at 7-Eleven. ( Four Corners )

While in Australia, students are only allowed to work 20 hours a week.

Many workers have told the ABC that they would be forced to work 40 hours and paid for only 20.

So while their base wage is $24 an hour, they would effectively only receive about $12.

Many others did not receive penalty rates and were threatened with losing their visa if they complained.

Prakash Kumar managed a Brisbane store and said there were many overseas students like himself who were systematically underpaid by store owners.

"I was getting paid $10 flat, no weekend rates, no penalty rates, nothing. It was just $10 for day and night whatever," he said.

Many stories only came to light after consumer advocate Michael Fraser started asking questions.

"I've been to 60 stores in three states and spoken to 100 people, every single person has been underpaid."