The High Court has given two members of Fine Gael permission to challenge the Government's failure to call by-elections in Waterford and Dublin South.
The court granted applications by Senator Paudie Coffey, Fine Gael's candidate in Waterford, and Michael Van Turnhout, the constituency chairman in Dublin South, for permission to take the challenges.
The proceedings arise following the judgment of High Court President Mr Justice Nicholas Kearns in a successful case taken by Sinn Féin Senator Pearse Doherty relating to the Donegal South-West by-election.
The seat in Waterford has been vacant since Martin Cullen resigned on 8 March this year.
The seat in Dublin South has been vacant since George Lee's resignation on 8 February.
Senior Counsel Frank Callinan said they were anxious to have the case heard as early as possible.
The proceedings will be mentioned before the High Court President on Thursday when Mr Doherty's case is also due to be mentioned.
Lawyers for the State have indicated that they will lodge an appeal against the Doherty judgment with the Supreme Court immediately after the matter is mentioned.
They said the Government intended to seek an early hearing in the Supreme Court.