One-in-three appeals to a federal tribunal over Centrelink's controversial "robo-debt" scheme have resulted in debts being set aside, a Senate committee has been told.
The Turnbull government copped fierce criticism last year after admitting to issuing automated recovery notices to 20,000 welfare recipients who were later found to owe less or even nothing.
More than 400 robo-debt cases have been decided by the Administrative Appeals Tribunal since July 2016, with just under two-thirds of debts upheld, a small number varied, and one-third set aside.
"For a third of debts to be set aside for those who had the courage to actually appeal should raise concerns about other debts," Greens senator Rachel Siewert said on Friday.
"I, for one, have not forgotten that there are many Australians still receiving incorrect or false debts to their detriment, and urge those that receive debt notices to interrogate and challenge the debt."
A spokeswoman for the Department of Human Services says people have been given ample opportunity to explain their circumstances throughout the debt-recovery program, and this option remains available.
"The reviews set aside by the AAT make up less than 0.1 per cent of reviews that have been completed with a debt," the spokeswoman said on Friday.
"The parties to such proceedings are able to provide the AAT with fresh evidence. That fresh evidence may lead to the original decision being set aside or varied."
The spokeswoman pointed out the commonwealth ombudsman last year found it was "entirely reasonable and appropriate" for the department to ask welfare recipients to explain data-matching discrepancies.
The ombudsman also found debts raised through the controversial program were consistent with earlier manual investigations.