Centrelink's bungled robodebt recovery program will be investigated by a Senate committee today, with representatives from the tax office and department of human services among those to be grilled.

Thousands of Australians were wrongly told they had to pay back money, after a mid-2016 decision by Centrelink to move to automated crosschecking of tax and welfare records.

The fallout from that money saving measure has been roundly criticised, and Greens senator Rachel Siewert's motion for a Senate inquiry into the controversial system was supported by Labor and the Nick Xenophon Team.

The Australian Council of Social Service (ACOSS) will be among those to present evidence to the committee today, after warning the roll out of automated debt recovery could cause significant distress and unjust outcomes.

"We would not see this kind of debt collection process in any other kind of corporation environment," ACOSS chief executive Cassandra Goldie said.

"Unfortunately when this program was released, it was just seven weeks out from Christmas. We had 20,000 letters going out per week — to date we think over 200,000 people have been affected by this.

"On the Government's own figures, at least 20 per cent of these so-called 'discrepancy notices' have been incorrect.

"We cannot know exactly the scale of how many people have been adversely affected. We don't know how many people have felt intimidated and entered into agreeing to repay debts they didn't believe they owed. We don't know how many more are inaccurate."

The Community and Public Sector Union (CPSU), which represents those employed by Centrelink who have had to deal with the complaints and compliance since the rollout of the program, warned the problems went further.

"Where you have government and the departmental management more focussed on denying there is a problem than actually fixing it, the results are obvious," CPSU national secretary Nadine Flood said.

"We've seen a bandaid on robodebt while the real problems are still there.

"We'll be raising in this inquiry the real experience of thousands of DHS staff who tell us the robodebt program is hurting their customers and is part of systemic problems across Centrelink and other DHS services."

Human Services Minister Alan Tudge has told his department to ensure welfare recipients can launch an internal review of their payments before debt proceedings are launched.

But he has insisted the program was working, and had identified close to $300 million in overpayments to welfare recipients.

Last week, Labor human services spokeswoman Linda Burney referred Mr Tudge to the Australian Federal Police (AFP).

Ms Burney wanted the AFP to investigate whether the minister and his department broke the law by disclosing a welfare recipient's personal information to a journalist, after she criticised Centrelink's debt recovery program in an opinion piece for Fairfax Media.