An Post has said the 24-hour strike by workers from midnight tonight will not achieve anything other than to cause further damage to the company's business and reputation.
A spokeswoman said the strike called by the Communications Workers Union (CWU) "won't achieve anything and won't change anything.
A spokeswoman for An Post
"It purely disrupts customers and will further undermine our business," she said.
The comments were echoed by Progressive Democrats senator, Mr Tom Morrissey this evening.
"The same problems will exist again on Thursday. The only difference is that there will be a huge backlog of post, and thousands of customers will have been inconvenienced," he said.
"It is time now for the Communications Workers Union (CWU) to face the reality that we are operating in a very different business environment, and companies must adopt and change to survive," he added.
Some 93 post offices operated by An Post will close tomorrow and mail sorting and delivery operations will also be disrupted from midnight for 24 hours.
However, the company said 1,400 sub-post offices throughout the State will be open tomorrow. Many of these handle social welfare payments.
Today is the deadline for staff at An Post's parcel delivery service SDS to express interest in a voluntary severance package. The business will be reintegrated into the main An Post company with the loss of 260 jobs.
An Post said initial applications had exceeded 260 and expressions of interest were coming "thick and fast".
The CWU yesterday accused the company of misinforming customers about the dispute. It said the 24-hour stoppage had been organised to secure pay rises due to 10,000 workers and pensioners under the Sustaining Progress agreement.
It was also aimed at seeking an "honest and open" public debate on the future of the postal service. Such a debate should focus on the real financial position of the company, the company's investment strategy and the type of service stakeholders wanted amongs other issues, CWU said.
The Labour Relations Commission reconvened talks in Dublin this morning on an ongoing row over postal services in Galway.
That dispute centres on overtime arrangements, An Post said. The union has lifted its overtime ban, which resulted in a major backlog of mail at the weekend. An Post said there was a backlog of around 60,000 items to be sorted.
A spokeswoman said the Galway dispute essentially involved staff claiming overtime payments for "ghost work".
She said An Post had no problem paying workers for overtime actually done, but that staff wanted the right to claim a basic overtime payment even where that overtime wasn't available.