Staff at the Cork Mail Centre in Little Island say they feel "betrayed" by the decision to close the facility and have vowed to continue to fight the closure.
A group of more than 100 workers are to take to the streets in protest this Saturday to raise awareness of the decision to close the centre.
Last month, An Post announced that the Little Island mail centre would close. The decision will result in more than 200 job losses. More than 100 of the affected workers have formed the Cork Mail Centre Action Group, vowing to "fight the closure and defend our jobs".
They will stage a protest march this Saturday at 2.30pm, starting at Grand Parade in Cork and have urged the public to come out and support them. They say that the decision to close the mail centre will have significant impacts across the board. In addition to the job losses, they say that it could undermine elements of the postal service, such as next-day delivery.
John Ahern, a spokesperson for the group, said that the postal network "can't take the hit" as it will result in the centralisation of sorting of all packages and post.
He described the closure as "ill-considered".
Workers have been offered redeployment or redundancy by An Post but Mr Ahern said that staff are unhappy with the proposals.
"We don't believe that there are enough vacancies to redeploy all of us," he said. "There are also issues of people going in and asking about redundancy; few of the staff will get the two-year package they say is offered."
The group held a press conference at the Imperial Hotel in Cork, where staff spoke out about the impact of the announcement of the closure.
Norma Creech, who has worked at the centre for 14 years, said she is "very annoyed, very stressed" since being informed.
"I am 61 years old," she said.
"I am very concerned about my future. I won't get another job at 61."
Her colleague Adrienne Sheehan turned 62 in recent weeks. She said she was "horrified" to see the sliding scale offered to workers in terms of redundancy, with those over 60 offered less than those under 60.
"It is total ageism and it is contrary to what An Post profess as an equal opportunities company."
She said the offers have been "totally at variance" with what was expected by the staff.
Charlotte Gillis said the Cork workers 'are a family' adding the atmosphere in the facility was tense since the announcement.
"Three weeks on, we have had so little information that we can't plan," she said.
"It is tense and stressful; people are heartbroken. We paid our union fees for years and there is no protest."
She said she received a message through Viber to tell her that her job was gone.
"It was half ten at night and it just said 'Cork closed'. Our whole lives are upside down. I still have a mortgage to pay, my youngest child is just starting school. These packages mean nothing to me."
The staff say that the Cork centre is so busy that it makes "no sense" to close it and that doing so will have a knock-on effect on the entire postal network, potentially undermining the smooth operation of the likes of next-day delivery due to the need to centralise all sorting.