DART passengers are likely to face overcrowded carriages at peak times because of a shortage of carriages.
Unless Irish Rail resolves an ongoing dispute with DART drivers, commuters will be affected on peak time routes on both sides of the city.
There was chaos this morning as passengers attempted to board crowded carriages travelling from station platforms on DART lines into the city.
And there is likely to be a repeat of the scenes this evening if negotiations today between Irish Rail and SIPTU do not resolve the ongoing dispute.
Speaking on RTE'S Morning Ireland, Barry Kenny of Irish Rail admitted “severe disruption” was being caused.
He said carriages were significantly shorter as a result of the dispute between DART drivers and senior management.
“Unfortunately we have unnecessary disruption today.
“It is likely to be in the order of 50pc of normal peak time capacity.”
He said the problem arose as DART drivers were no longer willing to carry out “coupling checks” on the trains – a process which takes about a minute.
Mr Kenny said since last month, DART drivers have been asked to carry out the “coupling check” on the trains before they leave the depot.
“A member of staff goes to the rear of the train, opens the door and the driver verifies that a light goes out in the cab and then checks that the train takes power.”
SIPTU say the job should be performed by maintenance.
“We have had ongoing talks and contact and will be talking again today. We don't want it affecting evening peak (services),” Mr Kenny said.
Irish Rail said DART tickets cannot be used on bus services.
SIPTU were not commenting on the ongoing industrial dispute this morning.