Fares on 14 Bus Éireann's Expressway routes are set to increase by around 5% from the end of this month.
The company said the fare changes are being introduced to offset "the rising costs on the business" and to encourage customers to buy their tickets online.
In addition return tickets will no longer be sold on board buses, but will be available online or at ticket vending machines.
Bus Éireann CEO Stephen Kent said it is part of efforts to move customers online where they can avail of cheaper costs and reserve seats in advance.
Speaking on RTÉ's Morning Ireland, he booking seats will enable the company to plan and deploy the right resources.
Mr Kent added that customers can avail of better deals if they book online, including a 33% early bird discount if tickets are bought online at least seven days in advance.
He said that passenger numbers are growing but the company is a commercial one that is dealing with increased costs, such as fuel, insurance and vehicle maintenance.
School bus fares and public service routes will not be affected by the changes, Mr Kent said.
