Serious disruption of Dublin Bus services is expected today when workers take to the streets to protest over redundancy payment levels.
Union leaders expect at least 5,000 to take part in the Dublin demonstration and several more thousand to join rallies at venues throughout the State.
A union source predicted last night that at least half of the Dublin Bus workforce would participate in the protest, causing major disruption to city services.
Construction sites are also expected to be badly hit, but other transport services, including the DART and mainline trains, are less likely to be disrupted.
Union leaders were unable to say with any certainty, however, what the overall impact of the rallies might be.
The protests were brought about by the refusal of several firms, including the Irish Glass Bottle Company in Ringsend , Dublin, to meet pay awards recommended by the Labour Court for staff being made redundant.
Former IGB workers will lead the Dublin march from Smithfield to Leinster House this afternoon.
About 370 staff lost their jobs when the company closed in July.
Talks aimed at resolving the payments row at the glass company were continuing at the Labour Court last night.
Employer representatives hoped that a breakthrough could lead to today's rallies being called off.
Union leaders said this would not happen, however, unless payments recommended by the Labour Court for workers at several other companies were also agreed, and the Government committed itself to improving statutory redundancy terms.
IBEC, the employers' representative body, condemned the rallies.
A spokeswoman said they would seriously undermine the planned talks on a new social partnership deal, due to get under way later this month.
A spokesman for Dublin Bus said it expected only minor disruption of services, as it understood that only off-duty workers were being encouraged to take part in the rallies.
City bus services in Cork, Limerick, Galway and Waterford, which are operated by Bus Éireann, may also be affected by the protests.
A spokesman for Iarnród Éireann said passengers should be prepared for possible disruption from midday, but the company hoped it would be avoided.
The demonstration at Smithfield begins at 2 p.m.
Rallies are also planned for Athlone, Bray, Cork, Clonmel, Dundalk, Galway, Limerick, Roscommon, Waterford, Carlow and Cavan.
The rallies are being organised by four trade unions: SIPTU, BATU, the TEEU and UCATT.