Up to 8,000 An Post workers will decide within two weeks whether to disrupt the national postal service over undelivered wage rises.
A national ballot on possible industrial action is due to begin today and run until October 14th.
The move was unanimously agreed yesterday at a special delegate conference of the Communications Workers' Union (CWU).
The ballot is being held over the company's failure to pay wage rises under the current Sustaining Progress agreement.
The Labour Court had recommended payment of the terms of the agreement but linked it to productivity changes.
The CWU said it believed this would make unreasonable demands on its members.
An Post said any threat of disruption to the postal service seriously damaged the company, customers and the economy in general.
A spokesman said: "This move is particularly irresponsible at a time when postal services are facing increasing competition at home and abroad.
The spokesman also accused the union of showing utter disrespect for the industrial relations institutions of the State.
But a CWU official said today: "This company owes staff and pensioners money. They're low-paid workers and it's not right or reasonable that they are expected to sponsor the postal service."
Under the Sustaining Progress deal, An Post was due to pay workers a staged 8.5% pay rise, beginning in November 2003, with a further 1.5 per cent increase due next month.
The company paid a 5 per cent increase in July following an assessor's report but has said it is unable to pay the rest unless changes in work practices and entitlements are made.
"We've exhausted all the avenues," a CWU spokesman added.
Last December, CWU members went on a one-day strike in protest at the closure of An Post's Special Delivery Service (SDS) division.
Around 110 SDS staff have since accepted voluntary redundancy and the remaining 160 have been redeployed to other work in An Post.
An Post made a €7 million profit this year following two years of major losses but has failed to reach agreement with the CWU on its restructuring plans.
The company said it would pay the wages owed under Sustaining Progress provided it could recover the full €60 million cost by eliminating what it said were outdated, inflexible and overtime-ridden work practices.