Nick Millington from Network Rail says people should find other ways to travel if possible
Transport chaos is forecast from today (June 21) as the majority of rail services across Wales will be suspended with railway workers striking in a growing dispute over pay, conditions and pensions.
The strike has been described as the "biggest outbreak" of industrial action in the industry in a generation.
With rail workers walking out on Tuesday, Thursday and Saturday, there will likely also be disruption on Wednesday, Friday and Sunday.
Britain's train operators have released plans for how their services will be altered during the week's rail strikes.
How are passengers in Wales faring with the strike action? Our reporters have been out and about across the country:
Which rail services in Wales are affected?
Transport for Wales: Most lines will be closed on strike days. On Tuesday and Thursday, a reduced service will run between Radyr and Treherbert, Aberdare and Merthyr Tydfil, with replacement bus services between Radyr and Cardiff Central. On Saturday, there will be limited trains between Radyr and Treherbert, Aberdare and Pontypridd, with replacement buses between Radyr and Cardiff Central. Transport for Wales is urging people not to rely on trains.
Wales and Borders: The majority of rail services across the network will be suspended, with the exception of services on the Core Valley Lines (CVL) north of Radyr in South Wales.
Great Western Rail: South Wales main lines will not be running on strike days.
CrossCountry: No services will run from Birmingham New Street to Bristol Temple Meads, Cardiff Central, Peterborough, Cambridge or Stansted Airport across the three strike days.
Avanti West Coast: North Wales will be impacted as a number of routes will not run and ticket sales have been suspended for the rest to the week to "help reduce disruption and overcrowding".
Due to strikes, the AA warns drivers in Wales to expect severe road traffic with more people using their cars this week. Some of the worst affected roads are predicted to be the M4, A55, A5 and A483.
It comes during a week of big UK events including Glastonbury Festival and Goodwood Festival of Speed.
Nick Millington from Network Rail urged people to check before they travel: "There will be a limited service, but it will be very limited.
"If you have other means of travel, if you can make alternative arrangements, that's our advice. And that's all the way from Tuesday through to next Sunday."
The Rail, Maritime, and Transport Workers union (RMT) says its members at Network Rail and 13 train operators will strike on three different days.
While Transport for Wales (TfW) itself is not in dispute with the union, the strike means it will be unable to operate rail services on Network Rail infrastructure.
Discussing the national rail strikes, a Welsh Government spokesperson said: "We strongly urge the UK Government to do all it can to resolve the disputes with the rail unions.
"While staff at Transport for Wales are not striking, the impact on rail services in Wales has been / will be extensive. Passengers should expect severe disruption and check advice from train operators before travelling."
The Welsh Government added: "We urge road users to plan ahead and allow more time for journeys, as roads may be busier as a result of the rail strike."