An Post last night advised customers not to post any mail until further notice, despite the expectation that industrial action at the company will be called off today.
An overtime ban by members of the Communications Workers' Union (CWU) began from midnight as planned, while a strike at the GPO in Dublin was also scheduled to go ahead.
But the union is expected to discontinue industrial action following an emergency meeting of its disputes committee today.
The meeting was called following a breakthrough in talks at Government Buildings with the National Implementation Body (Nib), which met the parties yesterday for the fifth day in succession.
It proposed that action be deferred while an independent assessment is carried out of cost factors in dispute between the two sides.
Both parties accepted the proposal, but An Post said the union's failure to immediately call off industrial action created uncertainty about services. As a result it was advising people not to post mail in any part of the country until further notice.
The CWU said it was unable to defer the strike immediately as it had to give committee members time to travel to Dublin for the meeting. The industrial action is over the company's refusal to pay the full terms of Sustaining Progress to 8,500 CWU members.
Independent accountants will be asked to assess the costs of the union's demands and report back to the Nib by next Monday. Social welfare payments will be made from the GPO today as normal, in spite of the strike there.