The public broadcaster must also fund a series of independent audits to make sure the six-year error is never repeated.

The Fair Work Ombudsman launched an investigation after the broadcaster admitted discovering instances of casual workers not receiving what they should.

In total, 1907 current and former workers - including reporters, presenters, make-up artists and camera operators - were underpaid $12,029,000, mostly between October 2012 and February 2019.

Underpayments for things like overtime and penalty rates ranged from $7 to $180,000. In some cases staff were paid less than the minimum hourly rate.

The ABC has already back-paid $11,983,950 to 1828 employees, with everyone to have their money by the end of July.

Fair Work Ombudsman Sandra Parker said the broadcaster had come forward to admit its mistakes, and there was nothing deliberate about it.

But she said: "The extent and duration of the underpayments are disappointing."

The ABC is now subject to an enforceable undertaking to fix the issues that caused the problem.

In addition to paying back staff and making a $600,000 contrition payment, it will have to fund independent audits of its workplace systems for the next three years.

It will also have to implement an electronic record-keeping and rostering system, and better train payroll and human resources staff.

Australian Associated Press