Former foreign minister Marise Payne will appear as a witness in an ongoing royal commission into the failed robodebt scheme.
Ms Payne was human services minister at the time the program was introduced, alongside then social services minister Scott Morrison.
The former prime minister will also face the inquiry on Wednesday as a witness over his role in the debacle.
On Monday, the commission heard from senior ATO staff who expressed concerns in 2017 that data provided by the tax office was being incorrectly used to calculate debts.
ATO director of data management Tyson Fawcett, who has been with the agency for over 30 years, explained averaging annual income data to arrive at a fortnightly rate did not work.
Last week, former Services Australia general manager of business integrity Mark Withnell rejected a statement the controversial income averaging process, also known as "income smoothing", was fundamental to proposals for the scheme.
Mr Withnell denied memory of a 2015 meeting at which it has been claimed he was frustrated when told an income averaging debt calculation practice was not lawful.
Another former public servant, ex-Social Services employee Catherine Halbert, denied in her evidence manipulating the truth about the department's view on the scheme in 2015, insisting it did not endorse income smoothing.
Meanwhile, former Human Services secretary Kathryn Campbell told the commission she knew law changes were needed in 2015 to use an average income instead of actual income for debt calculation, but said Social Services was in charge of the matter rather than her department.
