The Labour Party has warned that a referendum on abolishing the Seanad cannot be held on the same day as an election.
The Government is considering plans for the massive reform which could be put to the public in the spring.
But a Labour spokesman it would not be feasible to hold such a major poll while party political issues were also being debated.
"There are 60 separate references to the Seanad in the Constitution and all of them would have to be removed," a Labour spokesman said.
"It is quite a complex thing. This is not a simple one-line amendment.
"It's our view that the Government is flying a kite on this one."
Tony Killeen, Defence Minister, said that the future of the Seanad is to be discussed at the first Cabinet meeting of the new year.
There is speculation that such major political reform could further delay plans for a general election, expected in March.
Fine Gael leader Enda Kenny revealed in 2009 his intention to abolish the Seanad and cut the number of TDs by 20 if put in power.
Sinn Fein's Pearse Doherty, a former Senator, accused the Government of lagging behind public opinion.