Iarnród Éireann is set to shed at least 450 jobs, almost 11% of its workforce, over the next four years.
The decision is part of a cost containment programme aimed at tackling its deficit of €45.3m.
Iarnród Éireann is under pressure from falling passenger numbers and revenue, rising fuel costs and a cut in its government subvention.
Staff also face cuts in sick leave entitlements, subsistence allowances, and overtime under the programme negotiated at the Labour Relations Commission.
Since 2002, staff numbers have already fallen by a third - to 4,100.
The company recently opened a voluntary severance scheme aimed at securing 450 redundancies over the next four years - although it can't yet quantify what savings those job losses will deliver.
Meanwhile, unions and management have this week agreed a package of further measures aimed at delivering another €12m euro in savings.
They include changes to pension arrangements, overtime, annual leave, uncertified sick leave, and subsistence rates.
The company says these measures will reduce pressure to cut basic pay and deliver employment security.
Unions will ballot on the proposals by 20th June with implementation scheduled from the 9th of July.
But there's more to come at CIÉ - as cost reduction talks get underway at sister companies Bus Éireann and Dublin Bus next week.