Irish Rail has said it may have to introduce further 'pre-book only' services in the future as more people use the train.
The company says the practice is already in place for big events.
Passenger numbers are currently at record levels, but new carriages are not expected until 2021.
Irish Rail spokesperson, Barry Kenny, said it will not become a feature on regular services.
Advertisement
He said: "We are at that point between when we are expecting imminent approval from government for an order for new carriages, but it will be two years until those carriages arrive.
"(Pre-booking) is something we will have to consider looking at for more events, it's not something we anticipate on a general basis."
