Fresh rail strikes announced over the Christmas period will "significantly disrupt" passengers as the long-running dispute over pay, jobs and conditions escalates.
Welsh passengers have been warned to expect delays and cancellations over the festive period as further walkouts are confirmed.
Members of the RMT transport union will already go ahead with walkouts as planned on 13-14 and 16-17 December, as well as further strike action from 6pm on Christmas Eve to 5.59am on 27 December.
RMT workers will undergo various 48-hour strikes at both a national and regional level from next week throughout the month of December and into the New Year.
Those involved in industrial action are primarily workers from Network Rail, however the dispute means Transport for Wales trains will also be affected.
The rail service explained: "Transport for Wales is not involved in the industrial action. However, the industrial action resulting from the dispute between the unions and Network Rail means we’ll be unable to operate rail services on Network Rail infrastructure."
It added the strikes "will significantly disrupt the rail network across the whole of Wales".
The majority of rail services will be suspended on the following dates:
13 - 14 December
16 - 17 December
From 18:00 on 24 December until 05:59 on 27 December
3 - 4 January
6 - 7 January
Whilst it is not clear which lines will be affected specifically, Network Rail services include the South Wales Mainline from Swansea to Paddington via Bridgend, Cardiff, Newport and the Severn Tunnel, as well as the North Wales Mainline from Holyhead to Crewe.
The announcement comes after the union urged workers to reject the latest pay offer.
The latest offer for Network Rail workers included a pay rise of 8% over two years with a guarantee of no compulsory redundancies to April 2024.
Responding to the RMT's latest statement calling more strikes, the UK's Transport Secretary Mark Harper said: “It’s incredibly disappointing that, despite a new and improved deal offering job security and a fair pay rise, the RMT is not only continuing with upcoming industrial action but has called more strikes over Christmas.
“It’s especially disappointing given the TSSA union has described this new and improved deal as the ‘best we can achieve through negotiation’ and called off strikes.
“The Government has played its part by facilitating a fair and decent offer but, by instructing its members to reject it, the RMT has failed to play its part and our rail network now faces more harmful disruption rather than helpful discussion.”
The RMT will continue to hold talks with the Rail Delivery Group (RDG), which represents the 14 train companies, on Tuesday (6 December).