Thousands of rail passengers face disruption on Monday as a result of a planned 24-hour stoppage by line inspection and maintenance staff.
Iarnród Éireann said last night that routes which may be affected include Cork/Dublin, Ennis/Limerick/Dublin, Tralee/Dublin and Tralee/Cork as well as commuter services in the Cork region such as Cork/Cobh and Cork/Mallow.
The trade union Siptu said that rail workers were being forced to take industrial action because management was continuing to forge ahead with plans which undermined existing working conditions without agreement.
Siptu branch organiser Willie Noone said management was "progressively introducing a five-day week spread over seven days for certain categories of workers and utilising contract workers to carry out essential work which should be done by our members".
An Iarnród Éireann spokesman strongly denied that the company had breached any agreements.
He said that under a deal reached in 2000 line inspectors and maintenance staff were rostered on a Monday to Friday basis with some night-time work.
Staff employed after the agreement worked under more flexible arrangements while contractors were also used to carry out some night-time work, he said.
He added that a number of the pre-2000 staff were seeking to opt out of compulsory night work while at the same time seeking first option on other night work which attracted premium overtime pay.
The spokesman said that the issue had arisen among a handful of staff based in Cork. If the company agreed to the union claim, it could have to lay off up to 50 staff who have more flexible working arrangements, he added.
The company said it had engaged in extensive efforts with Siptu and another union, the NBRU, to resolve the dispute.
It said that the Labour Relations Commission had recommended that the issue should be referred to the Labour Court and that there was an opportunity for this to be heard in the week after next subject to the removal of the threat of industrial action.
"Iarnród Éireann urges Siptu and NBRU, and permanent way staff, to avail of this opportunity, and ensure our customers are not unnecessarily disrupted," it said.
Siptu said it remained available for talks over the weekend in an effort to resolve the dispute.