Sinn Féin, the Green Party and Independent TDs have criticised boundary changes which they say favour large parties.
They said the loss of a number of five-seat constituencies favoured "establishment" parties and would prevent new voices from entering the Dáil.
Mr Finian McGrath, an Independent TD for Dublin North Central, which lost one of its five seats in the changes, described the proposals as "an attack on democracy".
He said: "I want to represent the people of Dublin North Central and I will fight all the way on this issue. The people of this area will see what it is - it's an attempt to squeeze out a dissenting voice."
Mr McGrath, who will have to increase his personal vote by 10 per cent to hold on to his seat, ruled out taking legal action to challenge the changes.
Two Sinn Féin candidates, who performed well in the last election but missed out on a seat, Cllr Joe Reilly in Meath and Cllr Seán McManus in Sligo-Leitrim, appeared to lose out as their constituencies were reduced to three-seaters.
Sinn Féin's spokesman on environment and local government, Mr Arthur Morgan, described the changes as a backward step.
"It is something which will favour the establishment parties and prevent the emergence of new voices in Irish politics, making the Dáil even less representative than it currently is.
"In our submission, we called for a return to larger constituencies, as the number of members returned per constituency is a crucial component of our electoral system. We believe that a wider political spectrum is more democratic and representative. It is disappointing that such a position was not adopted."
The Green Party also said the trend of moving away from five-seat constituencies was regrettable. Party chairman Mr John Gormley said: "There are now 18 three-seat constituencies and 12 five-seat constituencies, making it more difficult for small parties and Independents to make a breakthrough."
However, Mr Gormley said the changes would not affect the Green Party's chances of retaining their Dáil seats.
Nevertheless, the reduction in seat numbers in Dublin North Central and Meath is a blow for the party which had been hoping for a breakthrough in these areas.
On the other hand, Mr Gormley said, the expansion of Kildare North to a four-seater made a seat gain a "distinct possibility".
"In the last election the Green Party targeted seats which yielded good results and this strategy will continue in the run-up to the next general election."
The changes are seen as likely to benefit Green Party TD Mr Paul Gogarty, whose Dublin West constituency has been increased to a four-seater.
