More than 20 major post offices, including the GPOs in Dublin, Cork and Limerick, were closed today due to what An Post says is an unofficial dispute by postal workers.
The action by members of the Communications Workers' Union (CWU) is an apparent escalation of a dispute that shut post offices in Cork last Friday.
An Post said the action would make it impossible for customers using the swipe-card system to collect unemployment benefit.
However, the Minister for Social and Family Affairs, Ms Mary Coughlan said this evening that those who were due to be paid unemployment assistance at post offices today would instead be paid tomorrow.
She said she had asked her officials to request a commitment from the CWU to restore services to social welfare customers and to keep these services outside their dispute with An Post.
An Post apologised for the inconvenience caused to customers by what it said was "unofficial industrial action by post office counter staff".
A spokeswoman said she would "completely refute" claims made to the media by the CWU that the dispute followed An Post's failure to recognise recommendations made by the Labour Court.
Members of the union had been balloted last year on plans to convert some of An Post's "least busy" post offices into sub-offices, she said. They had agreed these measures in a deal that included a 12 per cent pay increase.
A spokesman for the CWU could not be contacted for comment this afternoon.