Iarnród Éireann is to stop cyclists taking bicycles on board trains at peak times from today.
Bikes can travel on board at off-peak times, but only if booked in advance.
The ban is set to be enforced on all Iarnród Éireann trains, including the DART.
However, folding bikes will be permitted during peak times. The ban is being introduced at Heuston Station in Dublin first.
Communications Manager at Iarnród Éireann Barry Kenny said: "We have had increasing number of instances of people bringing their bike on peak times which has capacity issues and indeed safety issues.
"Our customers were giving us feedback where they wanted to see us apply this more strictly which is what we're doing from today, making it very clear for the benefit of cyclists and non-cyclists alike what is and not permitted."
Meanwhile, rail passengers intending to travel on the bank holiday Friday are still facing the prospect of serious disruption due to a three-hour stoppage scheduled by train drivers.
Five days of talks between Iarnród Éireann management and unions at the Workplace Relations Commission broke down early on Saturday morning.
However, following an invitation from the Workplace Relations Commission, Iarnród Éireann and trade unions representing drivers will resume facilitated talks on productivity issues at the WRC tomorrow afternoon in an effort to avert industrial action on 23 October and 6 November.
NBRU General Secretary Dermot O'Leary said: "We have accepted the invitation on the basis that the full complement of issues associated with the productivity agenda, inclusive of previous contributions of train drivers will be addressed."
Mr O'Leary went on to say: "There is an expectation from our members that their issues will be given the same consideration as those of the Company."
Iarnród Éireann has said that the stoppage between 6am and 9am would have a domino effect, causing knock-on disruption throughout the day - which is one of the busiest of the year.
