Irish Rail has warned customers to expect major disruption to services running each Saturday from Heuston Station.
Engineering works will be ongoing between Hazelhatch and Thurles on the Dublin/Cork line over the course of June and July, with a knock-on impact on several services.
The works will not clash with major events like sports fixtures and concerts but customers have been advised to double-check their bookings before travelling.
The project will be paused for the month of November but will resume in September and continue through the autumn months.
Those who already have a booking on an affected service will be contacted by Irish Rail and given the option of changing their travel arrangements or receiving a full refund.
Irish Rail has said that the €10m annual investment will lead to "higher reliability, smooth running of trains and consistent 160kph speeds".
You'll find a full list of dates and routes here.