On Saturday, Fairfax Media revealed that a single resources company transferred more than $11 billion to Singapore where the corporate tax rate is as lows as 2.5 per cent. Treasurer Joe Hockey is not keen on a Glencore/Rio Tinto merger . Credit:Graham Denholm Corporate tax in Australia is levied at 30 per cent. A string of mining companies have established so-called "marketing hubs" in Singapore as part of suspected efforts to minimise tax where they extract resources. BHP Billiton and Rio Tinto, Australia's biggest miners, are both operating mining hubs in Singapore. The names of the companies channelling money to Singapore were redacted by the Australian Tax Office in a document released under Freedom of Information and Senate committee chairman Sam Dastyari wrote to Mr Jordan on Tuesday requesting he reveal the names to the inquiry.

But Mr Jordan claimed "public interest immunity" in refusing his request, saying identifying companies could undermine confidence in the tax system. "The Treasurer has been consulted about making these PII [public interest immunity] claims, and has endorsed them being made by me as an independent statutory office holder. The grounds of the PII claim are as follows," he wrote in the letter, tabled at the committee's first public hearing on Wednesday. "Disclosure of the information to the Committee by the Commissioner of Taxation will harm the public interest by undermining public confidence in taxation laws and taxation administration. "Disclosure of the information will have a substantial adverse effect on the proper and efficient operations of the ATO, contrary to the public interest. "That harm outweighs any public interest in discussing the information in public hearings of the Committee. The taxpayer confidentiality provisions in the taxation laws were enacted by Parliament to protect inherently sensitive information relating to taxpayers' personal, private and financial affairs which is produced to the ATO for the sole purpose of administering the taxation laws."

On Wednesday, Mr Hockey pointed to past statements by Opposition Leader Bill Shorten and former Labor treasurer Wayne Swan, who both backed secrecy to retain integrity in the system. "The decision to disclose the information of taxpayers is entirely a matter for the Commissioner of Taxation as an independent statutory office holder," Mr Hockey said. "Confidentiality of taxpayer information has been a key feature of Australia's taxation system since the 1950s. The principle of confidentiality goes to the very essence of our voluntary, self-assessment taxation system. Without the continued application of confidentiality provisions, we run the risk of reducing compliance with the system." Mr Jordan conceded that the Parliament could demand the release of names but said such a move by a committee would be unprecedented. He said tax confidentiality encourages taxpayers to disclose information voluntarily.

"In the absence of taxpayer confidentiality the effective and efficient administration of the taxation system would be undermined by taxpayer reluctance to disclose information," he wrote. "In enacting the taxation confidentiality provisions, and following the long-standing convention of parliament only receiving and discussing taxpayer confidential information in confidence and in-camera, Parliament has recognised a public interest in maintaining the confidentiality of taxpayer information from disclosure in the public or political arena." Mr Dastyari told Fairfax Media: "[The ATO] has made a policy decision to not reveal this information and I believe they have made the wrong decision. "Under parliamentary privilege there is no reason why this information cannot be shared, through this inquiry, with the Australian public. The Labor senator says he will write to Senate clerk Rosemary Laing to see what powers the Senate has to challenge the public immunity claim that has kept the mining company names secret.

The Tax Justice Network, which has campaigned for transparency, hit out at the Coalition decision to keep the tax details of private companies secret. Assistant Treasurer Josh Frydenberg recently argued in the Coalition joint party room that disclosure could lead to kidnappings of owners. In its supplementary submission to the inquiry, Tax Justice said the move was of "significant concern" and that claims by companies that they faced harm were "outrageous". "A document obtained from the Australian Taxation Office under freedom of information has revealed that the private companies linked to Australian high wealth individuals have average profit margins lower than the other categories of companies (foreign-owned and Australian publicly listed) in the group that the legislation applies to," it said. Loading With Nassim Khadem