Mail deliveries will be cancelled in all parts of the State today as thousands of postal workers stage a demonstration in Dublin.
Post offices run directly by An Post in cities and main towns will also close for the day, disrupting payments to some 30,000 pensioners.
Union and management representatives, however, agreed arrangements yesterday to get welfare payments back to normal as quickly as possible tomorrow.
The Communications Workers' Union (CWU), which has organised today's 24-hour strike and "national day of protest", will consider its next moves at a meeting of its national executive tomorrow.
Further disruption before Christmas, however, is now considered unlikely. Instead, the next phase of industrial action is expected to take place in January.
Union leaders anticipate that at least 3,000 postal workers will take part in today's march from the Garden of Remembrance at Parnell Square to Dáil Éireann.
The march, beginning at 12.30 p.m., takes place on one of the biggest pre-Christmas shopping days in the capital. A Garda spokesman said shoppers should take the march into consideration when making their plans.
The strike is over what the CWU claims is "a catalogue" of breaches by An Post of union-management agreements.
Mr Seán McDonagh, the union's national officer for An Post, said its main aim was to secure pay increases due under Sustaining Progress to staff and pensioners since November last year.
It was also seeking an "honest" debate about the future of the postal service.
The company has pleaded inability to pay the increases, a decision that saved it €22 million this year and means it is now likely to break even having earlier forecast heavy losses.
A spokesman for An Post said the Sustaining Progress partnership deal set out procedures under which unions could challenge employers' pleas of inability to pay increases. These provided for cases to go to independent binding arbitration where agreement could not be reached.
"The union has had that option since last November, and it hasn't used it. Its action today is disgraceful, and completely unjustified."
A row over Christmas overtime arrangements in Galway was resolved yesterday in talks at the Labour Relations Commission, and deliveries in the area are returning to normal.
Meanwhile, An Post said yesterday it had received 280 expressions of interest in a voluntary severance package from workers in its parcels division, SDS, which is to close with the loss of 270 jobs.
The CWU is opposed to the closure, but is engaged in talks on the issue with management, chaired by the former Irish Congress of Trade Unions general secretary, Mr Peter Cassells.
