An Post has said the closure of its mail centre at Little Island in Co Cork is unavoidable, given the steady and ongoing decline in the volume of letter post it handles.
More than 200 jobs will be lost when the centre closes next March.
The company said the decision had been taken in response to an annual drop of around 7% in the volume of letter post it handles.
The closure has been described as "devastating" by the Communications Workers' Union.
An Post operates four mail sorting centres, with one each in Dublin, Athlone, Portaloise and Cork.
One of the four has been earmarked for closure by the company as part of a cost-cutting review that had been ongoing since 2017.
Cork, the newest of the four centres, is the one to lose out.
Management announced news of the closure at an overnight meeting with workers.
The closure be carried out on a phased basis, beginning in September.
An Post said that would result in the loss of 216 jobs which, accounting for part-time workers, will affect 240 people.
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The company said the Little Island centre was operating below a quarter of its capacity and the closure would result in savings of €11 million per year.
It also said it would invest €15m in its parcel infrastructure in Cork, where volumes are increasing dramatically due to the growth of online shopping.
Staff at the mail centre will be offered compensation of six weeks' pay per year of service, up to a maximum of two years' pay.
They will also be offered redeployment to other areas within the An Post network in Cork.
The Communications Workers' Union has called on the company to ensure that staff will be helped to rebuild their careers.
Speaking on RTÉ's Morning Ireland, CWO Deputy General Secretary Sean McDonagh said the decision was "devastating" for workers and their families.
However, Mr McDonagh said the possibility of closure at Little Island had been on the cards since 2007.
Because of this, he said, the union had been working with the company for some time and discussed how to deal with the immediate impact for employees.
Mr McDonagh said that a voluntary severance package and a redeployment programme had already been discussed.
He said that there were agreements for people to redeploy to "within 30 miles" of their current location. He added that all options will be discussed with workers over the next nine months.
At this point, he said, there were no concerns for the other sorting offices.
Mr McDonagh said that because of the decline in mail, the numbers of staff in all four centres had been incrementally decreased over the last number of years.
Also speaking on Morning Ireland, An Post CEO David McRedmond said he believed there would be enough jobs for those who want redeployment and opportunities will be found for those who want them.
Mr McRedmond said that a severance deal will be offered to other people.
He said that management were working closely with staff, adding that "we are nothing if we don't look after our staff".
He said that huge investment was being made in parcel deliveries but it was a different type of service.
Mr McRedmond said the parcel service needed to be developed in order for An Post to have a sustainable future.
"We're transitioning from a world of letter to a world of parcels. We're making a huge investment in the parcel network," said Mr McRedmond.
"The parcel network is a very different type of network. For example, we're taking postmen and postwomen off bicycles and putting them in cars and we're putting a whole new electric fleet into Cork, to be able to do that.
"Most parcels in the country in the country, 80% of them, come through Dublin. It's a very different pattern, parcels."
He said discussions about the site have taken place with the IDA and said An Post will work with the Land Development Agency.
