A more aggressive approach to debt collection by the Australian Taxation Office, as it plays its part in returning the Australian government budget to surplus, has emerged as a significant risk factor for lenders in the micro and small business segments.According to research conducted jointly by Macquarie Research and East & Partners, money owed to the ATO has grown from around seven per cent of total collections, in 2008, to the current level of 10 per cent. This ratio has increased 100 basis points over the past year and is close to the peak in 2010.These figures include insolvency-related debt. Excluding impairment provisions, the ratio of "collectable" debt to total collections has increased from around 4.5 per cent in 2008 to 5.5 per cent currently.The increase suggests that there is "ongoing stress" in the economy, according to Macquarie and East.Most of this "lending" is to the micro business and small business segments, which account for two-thirds of the ATO's collectable debt. Money owed to the ATO totals about A$11 billion, with the bulk of individual loans being worth less than $2 million.About 10 per cent of all money owed by small and micro businesses is owed to the ATO, according to the report.As the Government pushes for a budget surplus, the ATO "credit facility" is being closed off. This creates a risk that more small businesses will become insolvent.Macquarie and East said that the number of insolvencies initiated by the ATO had increased from 3.3 per cent, in 2008, to the current level of 6.3 per cent.The consequence for the major banks is likely to be higher bad and doubtful debts.The report said National Australia Bank had the greatest exposure to ATO-related business failure, followed by Westpac.