Ireland is sixth-worst for tax-dodging by big corporations
Ireland has been ranked in the top 10 tax havens for big business.
Oxfam branded the Republic the sixth-worst country for helping corporations to cheat their way out of billions of euros in tax bills each year.
The development agency said p rofit-shifting, sweetheart deals and a lack of effective tax-dodging rules influenced the damning score.
Jim Clarken, chief executive of the charity's Irish division, said the country is part of a toxic global system that services the very wealthiest while ordinary people pay the price and lose out on essential public services.
"Around the world, we are known as a country of good fun, bad weather and awful tax policies that facilitate worsening inequality by allowing some of the world's richest companies to avoid paying their fair share to society," he said. "This is no badge of honour."
Bermuda was ranked the worst in a study of 15 countries, followed by the Cayman Islands and the Netherlands.
Switzerland and Singapore were ranked in fourth and fifth place followed by Ireland, with Luxembourg, Curacao, Hong Kong and Cyprus making up the rest of the top 10.
The final five were the Bahamas, Jersey, Barbados, Mauritius and the British Virgin Islands.
The countries were ranked in Oxfam's new Tax Battles report, published on the same day an appeal hearing gets under way by whistleblowers behind the LuxLeaks affairs, which exposed sweetheart tax deals between Luxembourg and large corporations.
Oxfam said tax avoidance by multinational corporations costs poor countries at least $100 billion - about 92 billion euros - a year.
It said that money could educate the 124 million children who are not in school and fund healthcare to save the lives of at least six million children every year.
Oxam highlighted the tax paid by Apple in Ireland, which worked out at 0.005 percent, according to a European Commission investigation that also said the tech giant owed about 13 billion euros in back taxes.
Mr Clarken said: " Citizens everywhere have had enough. We need to get serious about making companies pay the tax that's due and we need transparency about where and how profits are made and where and how they are taxed.
"We collect more detailed data about farm animals in this country than we do about the tax affairs of multinationals."
Oxfam insisted the issue was not Ireland's relatively low corporation tax rate of 12.5%, but about loopholes and sweetheart deals.
It called on the Government to support and agree international criteria on what makes a tax haven and a clear public list of where they are along with sanctions to limit profit shifting.
Mr Clarken said: "Governments are falling over themselves to ensure corporations pay as little tax as they wish - and starving their countries of the money needed for education, healthcare and job creation in the process. They must ensure companies pay a fair amount of corporation tax, otherwise their citizens will continue to pay the price."
The Department of Finance rejects Oxfam's damning verdict.
"Ireland does not meet any of the international standards for being considered a tax haven. Ireland is fully compliant with all international best practices in the areas of tax transparency and exchange of information," it said.
The Government said the corporation tax rate and incentives do not make the country a haven.