A commission is to be established shortly to decide which constituencies will lose seats in next year's elections for the European Parliament.
Sources say it is likely Munster and Leinster will lose a seat each, but no official decision will be made until later this year.
Ireland has 15 MEPs, but this will be reduced to 13 because of EU enlargement.
The Constituency Commission will be established in the coming months and will include a High Court judge, the Ombudsman, the secretary general of the Department of Environment and Local Government, and clerks of the Dáil and Seanad.
The changes will be partly based on the latest census statistics and the commission is due to issue its recommendations in October.
Once established, the commission will operate independently and the public will be entitled to make submissions.
This redrawing of constituency boundaries may see Clare and Longford/Roscommon included in the Connacht/Ulster constituency, according to sources.
The Government agreed in January this year that Ireland's representation at the European Parliament be cut from 15 to 13, instead of the proposed 12.
The decision will be ratified at an EU summit in Greece later this month.
At present Dublin, Munster and Leinster have four seats each, while Connacht-Ulster has three.
The next election to the parliament will see an influx of new candidates, with at least five MEPs, including Niall Andrews (FF) and Mary Banotti (FG), signalling they will step down.
