Irish Rail is advising passengers that no drink will be allowed on board its Galway and Westport services out of Dublin on Monday morning and afternoon.
The trains also will not be selling alcohol from the catering trolleys.
The five services are expected to be busy with customers heading home after the Longitude festival.
It follows Irish Rail's move to ban people from drinking alcohol on those routes last year.
The ban came into effect from October 12, and is enforced every Friday, following regular reports of anti-social behaviour connected to excessive alcohol consumption.
It affects the Heuston to Galway routes departing at 11:25, 13:25 and 15:35; as well as the 14:45 train from Heuston to Westport each Friday.
"The vast majority of customers who wish to enjoy an alcoholic beverage on-board our services do so without impacting in anyway on their fellow passengers, but unfortunately there is a minority that do over indulge, particularly those travelling in large groups, who can disrupt others in a negative way," a spokesperson for Iarnród Éireann said at the time.
"There have been high volumes of complaints of such behaviour on these services so we have taken the decision to ban all alcohol from them."