The ABC on Thursday issued a statement revealing a review it started in January had uncovered some of its staff had been underpaid across three different areas.

Current and former employees who were employed under a buyout system between July 14, 2014 and June 20, 2021 were paid less than they were entitled to.

The system allowed employees to forego overtime and other entitlements in order to receive a higher wage.

Other staff incorrectly remained on a lower-paid classification or were underpaid meal allowances, the ABC said.

"The ABC will start paying what is owed after a period of consultation with affected individuals," the statement said.

"We are sorry to all those impacted by this error, which falls short of the standards expected of the ABC.

"The ABC has implemented several measures to ensure all employees are paid accurately in the future."

It did not disclose how many staff had been affected.

READ MORE:

The Fair Work Ombudsman would also not disclose the amount the broadcaster was expected to pay back its staff over that period due to the ongoing investigation.

The Community and Public Sector Union said it was "extremely disappointing" and was reflective of a serious cultural problem.

Union ABC section secretary Sinddy Ealy said funding pressures weren't a good enough excuse for bad management practices.

"It's time for the organisation to stop circling the wagons - they need to reign in the bad management practices that cause these problems and hold individual managers who have done the wrong thing to account," Ms Ealy said.

"CPSU members fully support the ABC cleaning up its mess and we will continue to work closely with the ABC's leadership to ensure the ABC meets its obligations as an employer to the highest standard."

The announcement follows a separate admission in 2019 forcing the ABC to pay around $12 million in backpay to 2500 of its casual workers.

It was triggered by a Community and Public Sector Union complaint, which referred the matter to the Fair Work Ombudsman in December 2018.