Park-and-ride charges came into effect at nine commuter train stations this morning.
Commuters will be charged €2 per day to park or €8 per week.
Motorists will see the cost of travelling to work rise by about €400 per annum as a result.
The stations where pay parking will be introduced today are: Dundalk, Drogheda, Laytown, Balbriggan, Skerries, Rush & Lusk, Donabate, Malahide and Portmarnock on the northern line.
Iarnród Éireann plans to introduce pay-and-display parking in 28 other rail and Dart stations from Longford to Gorey by November.
The other stations are Sutton, Killester, Clontarf Road, Booterstown, Dalkey and Bray. On the Heuston Station commuter line, charges are to be introduced in Athlone, Portarlington, Kildare, Newbridge, Hazelhatch, Carlow, Athy, Portlaoise, Clara and Monasterevin.
Coolmine, Maynooth, Mullingar, Edgeworthstown, Leixlip Confey, Kilcock, Enfield and Longford on the Maynooth/Longford line, and Arklow, Wicklow, Rathdrum and Gorey on the Wicklow/Gorey line will also have pay-and-display systems.
The stations will be policed by a private parking control and clamping company.
The plan, which CIÉ said would finance a car-park expansion scheme, was heavily criticised when it was announced in July with transport lobby groups branding it unacceptable.
Rail Users Ireland said it is considering taking legal action against CIÉ over the scheme although it is not clear on what that will be based.