More than half of all income tax collected by the state is paid by less than 10 per cent of taxpayers, according to new figures from the Department of Finance.
The figures, prepared by department officials for Dáil debates on the Finance Bill, show that the wealthy and the corporate sector are the biggest contributors to the tax take.
The top 2.5 per cent of taxpayers - just over 40,000 people who earn in excess of €100,000 - contribute 30 per cent of the income tax take.
The top 1 per cent of earners account for 20 per cent of the total income tax collected.
Although the figures are based on returns in 2002, the latest year for which a detailed tax breakdown is available, the proportions for last year are not expected to differ much.
They show how the income tax burden is increasingly slanted towards those on higher incomes. However, the figures also support claims that income disparity is widening.
More than 60 per cent of income earners - about 1.1 million people - are paid at or below the average industrial wage of about €30,000.
This group contributed less than 10 per cent of income tax.
By contrast, less than 20,000 people whose gross annual income was in excess of €150,000, contributed one fifth of all income tax. Along with Vat receipts, income tax is the most important generator of income for the government.
This year, the two taxes will contribute more than €12bn each out of a total tax take of €42bn. Corporation tax and capital gains tax together contribute about €8bn to government coffers.