"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 said.
"The complaint rate is running at 0.16 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."
Mr Porter criticised Labor and opposition human services spokeswoman Linda Burney for calls for the system to be shut down on a temporary or permanent basis, saying the opposition had no specific data about the number of complaints or levels of mistakes generated by the data matching.