More than a hundred train services were cancelled today because of unofficial industrial action by their drivers.
Arriva Trains Wales was forced to cancel services across its network after scores of drivers gave notice they would not be turning up for work in a dispute over pay and conditions.
The train drivers union Aslef, who are in advanced negotiations with the train operator, said they would not be supporting the one-day action.
"It is not something organised or condoned by the union," said an Aslef spokesman.
"I think the dispute is linked to pay and there are further meetings on Monday with regard to that."
A spokeswoman for Arriva Trains Wales said a shuttle bus service had been laid on between Carmarthen and Cardiff, via Swansea, but many other routes were cancelled outright.
Services will not be running between Cardiff Central and Shrewsbury/Crewe, Cardiff Central and Ebbw Vale, Aberystwyth/Machynlleth and Shrewsbury, Pwllheli and Machynlleth, Swansea and Shrewsbury (via the Heart of Wales), Treherbert/Merthyr Tydfil/Aberdare and Cardiff Central, Barry Island/Penarth and Cardiff Central, and Bridgend to Cardiff Central (via Vale of Glamorgan Line).
The Arriva Trains Wales spokeswoman said many passengers would have made aware of the severe disruption to their network through posters put up at stations, on-train announcements and media coverage.
"I think most people are aware it was happening," said the spokeswoman.
"We are hoping this (dispute) will be resolved and we are confident it will be resolved fairly shortly," said the spokeswoman.
She added: "It is inconvenient to our customers, there is no doubt about that. All we can do is apologise for the inconvenience these actions have caused our customers."