Virgin Trains East Coast staff have started a 24-hour strike in a long-running dispute over job security.
Virgin Trains said it will run a full timetable during the strike after contingency plans were put in place.
The RMT union said about 1,800 members, including train crew and some drivers, were taking action against threatened job cuts and disputes over working conditions and safety.
General secretary Mick Cash said: "RMT will not sit back while nearly 200 members' jobs are under threat."
Virgin Trains said it was making changes to customer-facing roles which will see a "single person take responsibility for the customer experience on our trains". The rail operator added this will have no impact on safety.
David Horne, managing director for Virgin Trains on the east coast said, “We have worked hard to ensure there are comprehensive contingency plans in place and I want to reassure our customers that our timetable will be unaffected during these walk-outs, as well as during any subsequent strikes by the RMT.
“The changes we are making are part of the customer-centric revolution we have planned for the east coast. We’re already more than half-way through our complete refresh of our trains with all new interiors being rolled out, and in two years will have our brand-new Azuma trains coming into service. Alongside more modern trains, we want a modern customer service proposition – one that focuses firmly on the customer.
“With our guarantees that there will be no compulsory redundancies, no impact on safety and a full timetable in place during the walk-outs, this strike will cost RMT members pay for no reason, and we urge the union to rejoin us around the negotiating table.”