Up to 200 post offices are at risk of closing in the next 12 months unless the Government puts financial support in place, an Oireachtas committee has heard.
The Irish Postmasters Union (IPU) laid bare the impact if the Government does not continue with the transformation payments.
The group told the Oireachtas Transport Committee that up to 25% of the entire postmaster network could be gone in the next year.
Irish Postmasters' Union general secretary Ned O'Hara said that, as more postmasters retire, the service will become "non-existent".
Postmasters in Ireland are contractors and are paid for the transactions in post offices.
Transformation fees are to expire at the end of June, and postmasters have warned that the service faces a cliff-edge if the Government does not put in place a financial intervention.
Mr O'Hara said:
"Decisions need to have been made and actions taken before then."
A report commissioned by Grant Thornton warned of "unrestrained post office closures" after June 2021.
"Their analysis recommended an annual Public Service Obligation (PSO) of 17 million euro, which it said would represent value for money for the State and provide a return of between 334 euro and 776 million euro," Mr O'Hara added.
Fianna Fáil Senator Timmy Dooley said that communities across Ireland have seen the "really negative impact" of post office closures.
"It is effectively removing a key core component of any village," he added.
"There is difficulty in maintaining a post office purely based on transactions because people are doing a lot more online, but the fact is that there are still some people who need that face to face opportunity to do transactions.
"While that demand exists, there is an encumbrance on the State to provide the service.
"The real crisis is now and this money needs to be in place by June.
"The only way to proceed is to make a very clear demand of Government that a public service obligation be put in place as a first measure to ensure we don't see the closures of any more posts office.
"We need to see the haemorrhage stopping and draw a line under the closures."
Fine Gael's Joe Carey said he is a "strong advocate" of the public service obligation.
"It's the only option available now to sustain the current chain of post offices we have," Mr Carey added.
"There is a urgency in this, we need to stand by the postmaster office unions."
The committee was told that since the Grant Thornton report was completed at the end of last year, 11 post offices have since closed.
Mr O'Hara said that postmasters make about 95% of all post offices nationally.
He said he believes over the next 12 months, up to 200 postmasters will retire.
"The risk is that they will retire from the busier post offices and they are the backbone of the network, and if that backbone is broken, the model is broken," Mr O'Hara added.
"It will be non-existent."
Sinn Féin's Darren O'Rourke said: "When anybody thinks of the fabric of Irish communities and what makes up an Irish community, in terms of infrastructure, the post office is very high on that."