Opposition Leader Bill Shorten has called on the Turnbull government to immediately suspend Centrelink's controversial automated debt recovery program, describing it as a "toxic mix of incompetence and cruelty" that has ruined Christmas for vulnerable Australians.

Mr Shorten, who is on summer holidays until the end of the week, has not previously commented on the project, which the government estimates will add an extra $4.5 billion to the budget. The automated system has been accused of miscalculating bills and sending debt notices to people who do not owe.

Stories have mounted in recent weeks of Australians – including asylum seekers and people with disabilities – who say they have been sent inaccurate debt notices.

Fairfax Media has spoken to one man who says he was sent an inaccurate debt notice for a period in which he was off work recovering from invasive brain surgery.