Workers on Virgin Trains West Coast have begun a 24-hour walkout – bringing disruption to some services.
Members of the RMT and TSSA unions are on strike in a dispute over pay, staffing and other issues.
There are five further stoppages planned – with action on Friday 22 December threatening Christmas travel plans.
Although Virgin is expecting to run a majority of journeys, there will be no trains from London to Edinburgh.
A replacement bus service is operating between Chester and Crewe while Arriva Trains Wales is accepting customers between Chester and North Wales.
However, trains connecting London with Liverpool and Glasgow are expected to run as normal.
Passengers are being warned to check before they travel and expect services to be busier than usual.
Image: The RMT and TSSA unions have attacked Sir Richard Branson’s wealth
Phil Whittingham, managing director for Virgin Trains West Coast, said: “The RMT leadership is attempting to cause disruption when many will want to travel by train to spend time with loved ones.
“We have explored a generous 3.6% pay increase, however the unions’ leaderships are insisting on 4%, double the 2% average increase seen across the UK this year.
“We know how important it is for friends and families to get together over the festive season, so whilst we’re sorry for the disruption we will keep the majority of our trains running with fully-trained staff onboard and at stations.
“We remain open to talks with the RMT and TSSA, and urge them to call off these strikes which will cost their members pay for no gain.”
Video: Sam Branson calls for hurricane aid
Both unions targeted Virgin founder Sir Richard Branson’s Necker Island retreat – recently devastated by Hurricane Irma – while insisting the company award equal pay rises to drivers.
TSSA leader Manuel Cortes apologised for disruption to passengers, adding: “We’re obviously happy for the drivers that they have had a decent settlement, but our members believe that they too should deserve a little more than a standstill inflation pay rise.
“Passengers and staff are keeping Richard Branson up to his Necker Island in luxury, while they pay more for fares and work harder for less.”
His counterpart at the RMT, Mick Cash, said: “Virgin is a wealthy outfit and there is no excuse whatsoever for Sir Richard Branson to undervalue and discriminate against the very same staff whose hard work finances his luxury lifestyle.
“All our members are demanding is a suitable and equal offer to that given to drivers to buy out their claim for a reduction in the base working week.
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“We have made it clear to the company that the inequality and underhanded approach of Virgin will be fought tooth and nail.
“The message needs to get through to Sir Richard Branson on his luxury island retreat in the sunshine that those who are financing his lifestyle through their hard graft have had enough and are prepared to fight for justice in theirworkplaces.”