Revenue has said it will be targeting pensioners on higher incomes following the announcement that 115,000 pensioners are facing tax demands this year.
Speaking on Morning Ireland, Revenue's Declan Rigney said individuals aged over 65 earning more than €18,000 a year or a couple in receipt of over €36,000 were liable for tax.
Mr Rigney said a person on a small occupational pension of around €100 a week was unlikely to be taxed.
He did not rule out back-dating the tax in some cases, but added that the focus of Revenue's resources at the moment was to sort out the issue this year.
Mr Rigney said there may be a review of some cases, but it was not an amnesty for taxes that had not been paid.
Revenue has issued information about the issue on its website.
The Minister of State at the Department of Finance, Brian Hayes, has said that in the great majority of cases no arrears will be due from pensioners who have been judged to own more tax to Revenue in 2012.
The Minister said a systems failure and a lack of communication between departments was behind the revelation that tax was not collected. It would be unfair if people had to pay additional penalties and interest based on previous years, he added.
The important thing is that pensioners are paying the correct tax in 2012, he concluded.
Meanwhile, revenue said it will provide an additional help-line service tomorrow for long-term pensioners and their advisors at the centre of the pension taxation controversy.
The 1890 numbers for various regions can be found on the letters sent earlier this week to 150,000 pensioners over the age of 65, to widows and widowers and to those on invalidity pensions.
A spokesperson said the help-line will remain open tomorrow from 9.30am until 4.30pm. It will resume normal week-day service will resume on Monday.
