Federal MP Anthony Albanese has joined with two of his constituents Tony Barbar and Curtis Dickson to take aim at the federal government over the new automated debt recovery system.
They are two in a growing number of cases that have emerged of people receiving written demands for money they say they do not owe.
"Malcolm Turnbull is the grinch who stole Christmas from some of the most vulnerable Australians in our community," Mr Albanese said.
"This Centrelink debt debacle has had an enormous impact on thousands of Australians."
Mr Barbar, 29, has been told he owes more than $4500 after he took sick leave from his job in 2010 to undergo chemotherapy for cancer, and now needs to prove he doesn't.
"He's an honest man," Mr Albanese said.
Mr Dickson, 31, was told he needed to pay back $750 in Austudy overpayments. He also says it was up to him to prove the claim was a mistake, and even so he was still required to go on a repayment plan before his matter has been reviewed.
"I really did feel like the onus of proof was on me," Mr Dickson said.
"I had a lot of doubt and anxiety about whether I had done the right thing, it has been quite stressful."
Ethnic groups, including the Federation of Ethnic Communities Councils Australia (FECCA), have warned it's an even worse scenario for migrants and refugees, some of whom have come from countries with intimidating and threatening governments.
"If English is your first language the letters are confusing and distressing enough, if English is not your first language then it can be almost terrifying," Director Emma Campbell said.
The government has defended the scheme, with Deputy Prime Minister Barnaby Joyce saying he would "make no apology for making sure that those who didn't need it, who got it, pay the money back," according to the ABC.
The Information Commissioner Timothy Pilgrim said his office is assessing Centrelink's data matching system which has let to the complaints, but no formal investigation is underway.
- with AAP