Rugby fans travelling to Cardiff to watch Wales vs New Zealand on Saturday 5 November, are being told not to travel by train following the announcement of strike action.
The RMT and TSSA unions have also said that industrial action will take place on Monday 7 and Wednesday 9 November as well.
Most trains across the Wales and Border network will be suspended, with Network Rail saying there will be 'severely reduced services' running east of Cardiff and to the valley lines, only.
The Autumn International on the 5 November is taking place at the Principality Stadium at 3.15pm. There will be no trains scheduled from Cardiff after the match, with the final service departing from Cardiff Central before 5pm.
Around 35,000 people are said to travel into Cardiff by train for international rugby matches, with more than 20,000 getting a return home.
Due to the strike action, inbound capacity by rail in the hours leading up to kick-off will be heavily reduced - two thirds lower than usual.
With severe restrictions on the trains, those travelling via road are being advised to leave plenty of time to travel and use park & ride facilities at CCFC Stadium in Leckwith or County Hall in Cardiff Bay.
Transport for Wales (TfW) is not involved in either dispute, but its services will be affected as it relies on Network Rail staff to run trains on much of the network.
Jan Chaudhry-Van der Velde, Transport for Wales Managing Director, said: “The safety of our passengers is always our primary concern and, due to the severe impact of the industrial action on our ability to run services, we are advising customers not to travel by train on Saturday 5 November and to make alternative travel arrangements.
“We’ll continue to work collaboratively with our partners to ensure we can support the event going ahead as safely as possible.”
GWR Customer Service & Operations Director, Richard Rowland, said: “We’re really sorry to all rugby fans who would normally be travelling with us to and from Cardiff Central.
“Unfortunately, due to the limited operating window caused by this industrial action, we’re unable to provide train services after the match and must therefore tell supporters not to travel to the game by train.”
Network Rail has said passengers can get ticket refunds if they are unable to travel on the strike days and can also use their tickets on alternative days.