US Senator Carl Levin has stood by his categorisation of Ireland as a tax haven, following criticism from Ireland's ambassador to the US.
In a letter to the senator, Ambassador Michael Collins said a US Senate subcommittee report on Apple's off-shore profit shifting was "wrong and misleading".
However in a statement, Mr Levin and Senator John McCain said that records show Apple paid tax in Ireland far below the 12.5% Corporation Tax rate and had a "special arrangement with the Irish Government".
"Most reasonable people would agree that negotiating special tax arrangements that allow companies to pay little or no income tax meets a common-sense definition of a tax haven," he said.
In his letter to the senator, Ambassador Collins rejected Mr Levin's previous assertion that Ireland was a tax haven, pointing out that none of the OECD's four key indicators of a tax haven applied to the country.
Mr Collins said Ireland was fully supportive of international efforts to address aggressive tax planning and was working with the US and OECD to address profit shifting.
He added: "We are also committed to play a leading role within the European Union during our Presidency in securing progress on a number of key files in the area of tax evasion and tax fraud."
Mr Collins also argued that the tax rates the senators attributed to Apple's Irish operations appeared to be calculated as if the company was tax-resident in Ireland.
This was despite the fact that the Senate committee's memorandum "clearly states that the companies concerned are not tax-resident in Ireland", he said.