A new partnership between An Post and Tesco will destroy the Irish post office network in two years, the Irish Postmasters' Union (IPU) warns.
As many as 3,000 jobs are on the line unless the Government make a clear plan to sustain post offices throughout Ireland, the group said.
It said that An Post would need to diversify its services if it was to survive a series of changes, including a move towards electronic payment systems.
The call comes following a new partnership between An Post and Tesco, which will see untrained staff, not bound by the Official Secrets Legislation, providing similar services to post offices throughout many of their supermarket stores around Ireland.
Brian McGann, general secretary of the IPU, said it wanted a government plan to sustain the post office network to be published and rolled out over the next three months.
A number of TDs and senators, including Lucinda Creighton, Michael Healy-Rae and Mattie McGrath, were briefed by the IPU on a Grant Thornton report on the Irish Post Office network in Dublin yesterday.
The report predicts the loss of 557 post offices across Ireland if the social welfare payment contract is lost and calls on the Government to create an action plan to save more than 3,000 jobs in the post office network.
An Post currently holds a two-year social welfare contract with possible extensions for up to four additional years.
However, the report highlighted that if social welfare payments moved to a system whereby they were paid directly into recipients' bank accounts by a direct electronic payments system; up to 444 post offices could be lost around Ireland by 2017, regardless of the current contract.
"There are lots of services that could be put through the post office.
"At the moment the post office network is over dependent on the social welfare contract. We need a plan," he said.
Postal workers are also concerned about the Government's move towards electronic payment systems as a part of its eCommerce strategy, saying that it is a huge blow to post- masters and to their employees.
The IPU also highlighted a variety of services, which the local post offices could provide at a fraction of current costs, such as motor tax renewal, which, it said, would save the taxpayer €60.6m over a five-year period.
The issue is to be the subject of a private members motion, which will be debated in the Dail next Tuesday and Wednesday.
Mr McGann expressed "grave concern" at An Post's partnership with Tesco to develop an alternative network, which he said had been made possible by the Government's inaction on the issue to date.
Mr McGann added that the partnership would "destroy the post offices network" in Ireland within just two years.
"To sustain the network the Government needs to act now," he said. "This is not simply a matter of economics, it is also a matter of social policy."
Between 2006 and 2012, some 209 post offices around Ireland closed.