Tax Commissioner Chris Jordan and a number of his senior colleagues have recently flagged concerns about cross-border transfers and intra-company refinancing and the potential that they are linked to tax avoidance. The Tax Office is particularly concerned about mining and energy companies extracting Australian minerals which have established "marketing hubs" in Singapore that appear to have little use other than as a destination for shifted profits. An ATO spokeswoman said the issue was currently under investigation. "I can confirm that we currently have 15 audits of marketing hubs under way with more ready to go," she said. Treasurer Joe Hockey is considering the introduction of a so-called "Google tax" but some experts fear the problem of tax avoidance and aggressive minimisation runs far deeper than the tech sector. Fairfax Media revealed this week that the 900 biggest companies in Australia reduced their tax bills by a combined $25 billion via deductions, exemptions and other concessions. The names of the companies have been redacted in the document, which is correspondence between the Singapore revenue authorities and their counterparts at the ATO, but a push is under way to use the powers of a Senate committee force the names of the multinationals into the public arena.

Hearings of the inquiry into corporate tax avoidance by the Senate economic references committee begin on Wednesday and will include witnesses from multinational miners Glencore and Adani, as well as Google, Apple, Microsoft and News Corp. Representatives of the big four accountants will also front the hearings as will former Tax Office adviser Martin Lock, whose submission to the inquiry details how "tax planners" engaged by corporations likely cost the public "billions of dollars" in lost revenue. "The difference between judicious 'tax planning' and 'tax avoidance' is usually blurred," he said. The Tax Justice Network and the union United Voice, which co-funded a report that showed the biggest Australian companies pay nowhere near the 30 per cent tax rate, believe the committee has the power to force the Tax Office to reveal the names of the companies moving billions of dollars offshore. "We understand the committee can make those documents public. Then people could know who the companies are that are shifting billions offshore and it would be up to those companies to explain why," said the Uniting Church's Mark Zirnsak, a member of Tax Justice. David O'Byrne, the national secretary of United Voice, said: "It is inappropriate that one company had $11 billion of related party transactions through Singapore and the Australian people do not know what company that is.

"If companies are claiming $25 billion of tax deductions from Australia's budget then we at least deserve to know who they are. If they won't identify themselves then it is up to the Senate committee to reveal them. "Until the ATO confirms who is responsible for this activity it is a slur on all companies."