The Revenue Commissioners have written to 1200 pensioners informing them that they may be liable for backdated tax.
The tax relates to pensioners who either did not declare their state pension or under-declared their income.
Revenue is individually assessing 2500 pensioners with incomes in excess of 50,000 euro a year.
RTÉ News understands that it has invited 1200 to carry out a self review of their total income and complete a new short tax return form.
Another 500 will also receive correspondence.
