For weeks now, Centrelink has been sending out thousands of debt notices to current and former welfare recipients.

It's part of an effort to claw back about $4 billion in welfare debt.

But many of the recipients say the new automated system is asking them to pay debts they don't owe.

Minister for Social Services, Christian Porter, denies there is an issue with Centrelink's automated system.

'Since the start of the financial year we've sent out 169,000 review letters. These are not debt letters. These are letters that use automated cross-referencing information from the ATO to information received at Centrelink, which shows there might be a discrepancy', he says.

'The complaint rate is running at .16 per cent. That's only 276 complaints from those 169,000 letters. That process has raised $300 million worth of money back to the taxpayer which was overpaid.'

'From what we've seen in a high volume system it's actually working incredibly well'.