Former Labour TD Joe Costello has said any newly constituted Dáil would be facing a costitutional crisis and would have to dissolve quickly after its formation.
Mr Costello was speaking after a High Court judge agreed to set a date for hearing his case over a failure to so far enact legislation to revise constituencies in line with population changes.
The case returns to court next Tuesday.
Lawyers for Mr Costello argue that if an election was called now, the make-up of the next Dáil would be in breach of the Constitution.
Article 16.2 of the Constitution says there must be one TD for every 30,000 people.
The 2016 Census showed the population had grown by 170,000 people nationwide since the last election.
Senior Counsel Conor Power told the court that the next Dáil could not remedy the situation. He said the only way would be for it to amend the legislation and dissolve itself, which was "unpalatable".
He said not withstanding what might take place elsewhere this case demands an early hearing.
Lawyers for the State told the court the legislation to revise the constituencies was published and could be passed by January or February.
Senior Counsel Frank Callinan said apart from difficulties arising from the fact the Government has no overall majority in the Dáil and Seanad, the actual implementation time for the legislation will be about one month purely on the administrative side.
He said 21 constituencies had to be changed and local authorities had to make changes to electoral registers among other things.
He said the necessary changes cannot be effected instantaneously.
The President of the High Court has now set a timetable for the state to lodge its defence to the case and said he will hear from both sides again next Tuesday before setting a date for hearing.
Yesterday, Mr Costello's lawyers said the Constituency Boundary Commission set up by the Government had recommended that there should be 160 members of the Dáil to take account of population growth but there are currently only 158 members.
Mr Costello lost his seat in Dublin Central at the last election when it was reduced from a four-seater to a three-seater constituency.
One of the Commission's recommendations was that the constituency should again be increased to four seats.
Senior Counsel Conor Power told Mr Justice Peter Kelly that if an election was held before this issue was addressed, then, from the beginning, the next Dáil, would have its constitutionality and authority questioned for being improperly constituted.
He said this should be addressed immediately.
The court was also told that Mr Costello was not looking for an injunction to prevent the Dáil from being dissolved.
But he was seeking declarations from it that the current ratio of TDs to the population breached constitutional requirements.
He is also seeking declarations that the Oireachtas members failed in their constitutional obligation to ensure constituencies are revised to take into account of population changes in the 2016 Census.
Speaking outside court Mr Costello said he was "pleased that the High Court has decided this is a matter of urgency".
He said even if the Dáil is dissolved today, there was merit in the case because of the constitutional issues involved.
Mr Costello said any new Dáil would face a constitutional crisis and be open to challenge.
He said a new Dáil "would have to deal with the question of a constitutional challenge, so the only way forward would be for a new Dáil to dissolve itself early and have a further election in line with proposed amending legislation which it has not passed and has been sitting on for six months".
Asked if he took any comfort from what was said in court about the legislation being "in train", he said the "problem is that it has not been passed and an election is looming".
