Yesterday the Australian Taxation Office gave headline details of its first automatic sharing of bank information with the United States Internal Revenue Service.According to the ATO, details of over 30,000 financial accounts worth more than A$5 billion are being provided to the US under the US Foreign Account Tax Compliance Act, known more widely by its FATCA acronym.In return the ATO will receive data from the IRS about Australians with financial accounts in the US and will use that data to detect cases of undeclared offshore income and tax evasion.Sharing of tax information with other jurisdictions, prior to the FATCA rules coming into force, has seen around A$250 million in additional taxes raised in each of the past two financial years.The cost to the Australian banking industry of implementing new FATCA compliant systems, on the other hand, has been estimated at A$500 million.According to Alexander Graham, a director in KPMG's banking practice, implementing  "the basics" for FATCA reporting at a major bank will cost between $40 million and $120 million. Major banks would need between 40 and 90 people working on development and implementation for 18 months to two years. Aside from these high systems development costs, the most pressing FATCA-related compliance issue for Australian banks has been the requirement to obtain a customer's self-certification of citizenship.And there are doubts over whether this first batch of data will be found to be completely accurate. According to Graham, some of the 30,000 accounts referred to by the ATO will be held by people for whom Australian banks have not been able to collect self certification details - that is, the bank has asked, as required under the FATCA rules, but was not provided with the documentation.He predicts that the end result will be clean data, once account-holders that are not intended to be caught by FATCA are excluded. However, it's likely to get tougher for most of the Australian financial services sector in the short term."We find in the Australian market, outside the majors and the other big banks, that the smaller second-tier banks and the smaller fund managers are not all that FATCA aware," Graham said.And there is plenty more bank account information yet to be gathered - assuming the smaller financial institutions are able to come to terms with the FATCA rules.