Woolworths has admitted to underpaying roughly 5,700 staff by up to $300 million.
The company, one of Australia's largest employers, says the mistake was due to non-compliance with the industry award.
According to the Sydney Morning Herald, Woolies undertook a review of their worker's salaries just before it introduced the newest enterprise bargaining agreement.
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It was during this review that the company noticed that there was a difference between what staffers were being paid as per their salary versus what they were entitled to be paid under the General Retail Industry Award.
"The review has found the number of hours worked, and when they were worked, were not adequately factored into the individual salary settings for some salaried store team members," the company said in a statement.
"Affected current and former salaried team members will receive their full entitlements, including back payments with interest and superannuation contributions, as soon as possible.
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"Interim back payments will be made before Christmas to affected Supermarkets and Metro salaried store team members for the two years reviewed to date (September 2017 - August 2019)."
The dodgy payments go as far back as 2010 and the amount is between $200 million to $300 million.
Chief executive Brad Banducci released a statement saying: "As a business we pride ourselves on putting our team first, and in this case we have let them down. We unreservedly apologise.
"The highest priority for Woolworths Group right now is to address this issue, and to ensure that it doesn't happen again."