The Revenue Commissioners have written to 1,200 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 2,500 pensioners with annual incomes in excess of €50,000.
It has invited 1,200 of those pensioners to carry out a self review of their total income and to complete a new short tax return form.
Another 500 will also receive correspondence.
