Dublin is to lose one seat to become a three-seat constituency in European Parliament elections, while Longford and Westmeath are to be transferred from the East to the North-West constituency.
The commission decided to share out the seats in accordance with the Nice treaty, which gave Ireland 13 seats up to 2009, and a fall thereafter - even though Ireland lobbied hard to have this reversed.
The reduction for Dublin will heighten the battle in 2009 and raise questions over Sinn Féin's Mary Lou McDonald's ability to retain her seat, following her failed Dáil campaign.
The commission said it could not give each constituency three seats without making some population changes because North-West would be massively over-represented.
The transfer of Longford and Westmeath into North-West will bring the swings into line, though it increases the odds of success for southern-based candidates in the next election.
Regarding the Dáil elections, the loss of 4,000 votes from Laois/Offaly will annoy many. It will not affect the constituency's balance, but it could significantly affect the seat share-out in Tipperary North.
The electoral areas from South Offaly will be shifted into Tipperary North under the commission's ruling, which defended its decision to breach county boundaries. Their departure will affect Fianna Fáil's Brian Cowen and Fine Gael's Olwyn Enright, though the losses suffered by both will probably cancel each other.
However, their inclusion into Tipperary North could sharply boost the chances of a Roscrea-based candidate for any major party, particularly Fianna Fáil.
The change had to be made because Laois/Offaly enjoys an 8 per cent over-representation, and neither is big enough to stand on its own.
The commission said it could have transferred territory into Galway East, but this would have breached the Shannon, or opt for Tipperary North, which was the easiest option.
Nearly 2,500 people living in rural districts around Stranorlar in Donegal will vote in Donegal South West, rather than Donegal North East following the boundary review.
However, the commission gave early warning that Donegal's hold on six Dáil seats could be in jeopardy in a future review: "If current population trends continue, the case for a reduction in Dáil representation in Donegal may arise for consideration in the future."
