Workers on Virgin Trains East Coast are staging a 24-hour strike today in a long-running dispute over jobs.
Members of the Rail, Maritime and Transport workers' union will mount picket lines after talks last week failed to break the deadlock. Virgin said it will run a full timetable despite the industrial action.
The union said around 1,800 of its members are involved in the row, including train crew and a small number of drivers.
General secretary Mick Cash said: "RMT will not sit back while nearly 200 members' jobs are under threat and while conditions and safety are put at risk by a franchise which is clearly in financial trouble.
"We will also not tolerate the cavalier attitude to safety that is now on show as the company mobilises its scab army of managers."
Virgin Trains said it had contingency plans in place to run a "normal and safe timetable" throughout the day on Monday. A statement said: "Virgin Trains is making changes to customer-facing roles which will see a single person take responsibility for the customer experience on our trains.
"This will have no impact on safety, and will result in a better experience for customers."
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.
"We're extremely disappointed with the RMT's decision to proceed with strike action when we have given assurances on each point raised by the union.
"On Wednesday, we agreed to the specific concessions set out by the RMT, but despite this they have decided to go ahead with today's walkout.
"The changes we are making are part of the customer-centric revolution we have planned for the East Coast.
"We're already more than two-thirds of the 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 today's walkout, this strike is costing RMT members pay for no reason, particularly as the RMT has agreed to hold further talks with us later this week."