Fianna Fail is prepared to pull the plug on the €3bn broadband contract if it gets into power, but won't spark a general election over the issue.
Party leader Micheal Martin is resisting calls from other opposition parties to end confidence and supply over the controversial plan to deliver high-speed internet to every home in the country.
At the same time, Mr Martin has said he wants to set up a new agency within the ESB to roll out broadband.
The Government is still up to six months away from signing a contract with the Granahan McCourt consortium.
In some of his strongest criticism yet of Fine Gael, Mr Martin asked: "What planet are they on?"
He accused Finance Minister Paschal Donohoe of "playing fast and loose with the public finances" and claimed the credibility of the National Development Plan is "in shreds".
However, the Cork TD insisted the Brexit situation remains "fairly volatile" and therefore too "severe" for him to force Taoiseach Leo Varadkar into a general election.
Responding from Romania, Mr Varadkar said: "To me, what I heard Micheal Martin saying to people in rural Ireland was, wait longer. People in rural Ireland have been waiting long enough."
He denied there was a cheaper or faster way of delivering broadband to all homes than the approach being taken.
The battle for rural Ireland will be played out on the doorsteps ahead of the local elections on May 24.
While ministers claim the timing is coincidental, opposition parties believe it is an attempt to buy the election with a flawed promise.
Social Democrats co-leader Catherine Murphy said this should be a "make-or-break moment" for confidence and supply.
"It is one thing for Fianna Fail to talk about this issue, but what it does about it is quite another. That will be watched very closely," she said.
"I do not play those political kinds of games. I rarely say that kind of thing about Fianna Fail, but this is a significant issue. The timing of this announcement is really quite cynical."
During a three-hour Dail debate, Communications Minister Richard Bruton faced questions over the cost of the project, input from the consortium and ultimate ownership of the infrastructure.
Fianna Fail's Timmy Dooley suggested Granahan McCourt is only putting between €300m and €400m into the project.
"My assumption is that thereafter the rest will be by way of debt or syndicated debt. We are also conscious the project will generate somewhere in the region of €1.5bn to €2bn over the life of the contract," he said.
However, a split has emerged in Fianna Fail over the ownership of the fibre lines at the end of the 35-year contract.
The Government intends to provide a subsidy for the upkeep of the network for 25 years, at which point the company must take the full risk for another decade. It will then own the infrastructure.
Mr Bruton says this will reduce the liability on the State, but Mr Dooley claimed this amounted to a "rather bad deal".
Public Accounts Committee chairman Sean Fleming said his colleagues "don't appreciate" that Eir already owns the telephone poles along which fibre cables will be run.
"I would ask the people of Ireland, do you really want to own a 35-year-old cable that has been blowing in the Irish weather for 35 winters?" Mr Fleming said.
"It could be a liability to the State to own that at that particular time."