The secrets of how Apple avoided billions of dollars taxes lie in a low-slung building of glass and brick in the hills of County Cork.
There, in the Hollyhill Industrial Estate and elsewhere in Ireland, Apple employs a mere 4 percent of its global work force. But there, too, Apple recorded a staggering 65 percent of its worldwide income — $26 billion last year — enabling the company, according to Senate investigators, to markedly reduce its tax bill in the United States and the rest of the world.
Such arrangements are not uncommon in Ireland, where for years authorities have not only tolerated but encouraged multinational companies like Google, Facebook, Pfizer, Johnson & Johnson and Citigroup to set up shop and provide good jobs, in return for helping those companies pay less tax around the world.
But on Tuesday, as Timothy D. Cook, Apple's chief executive, found himself on Capitol Hill being questioned about Apple's tax practices, Ireland came under sharp criticism for its attractiveness as a pied-à-terre for American companies doing business in Europe. At the eye of that storm: a special corporate tax rate of only 2 percent that Senate investigators say Apple worked out with Irish tax authorities.
(Read More: Ireland Says Not to Blame for Apple's Low Tax Rate)
Carl Levin, the Michigan senator who heads the Senate Permanent Subcommittee on Investigations, said Apple was "exploiting an absurdity" by using three Irish subsidiaries to legally avoid taxes.
The United States Senate is hardly Ireland's only critic on tax matters. Britain, France and other European Union countries have long been annoyed by Irish policies. During hearings in the British Parliament last week, Margaret Hodge, a member of the opposition Labour Party and chairwoman of the Public Accounts Committee, which oversees taxation, upbraided Matt Brittin, Google's vice president for North and Central Europe, that the company's tax practices were "devious, calculated and, in my view, unethical."
Even before the Senate subcommittee invited Mr. Cook to testify, the British prime minister, David Cameron, declared that the topic would be a focus of the meeting of the Group of 8 richest countries he plans to convene next month at Lough Erne in Northern Ireland.
"We need a truly global solution," Mr. Cameron wrote in a letter to Herman Van Rompuy, president of the European Council, in April. "As I am sure you will agree, the path to reform starts with the basic recognition that current global tax rules do not reflect the modern and globalized economy that our citizens live and trade in."
Ireland, with an economy that ranks 47th in the world, is not a member of the Group of 8.
Ireland's deputy prime minister, Eamon Gilmore, on Tuesday disputed the Senate report's contention that Apple paid a special rate, saying "Ireland doesn't negotiate special tax rate deals with any companies." He said that if Apple was not paying its fair share elsewhere in Europe, the fault lay in "loopholes" in other European countries that make it too easy for companies to avoid taxation.
"That's an issue that has to be addressed first of all in those jurisdictions," Mr. Gilmore told reporters in Brussels.