A rail operator was running a limited service on Sunday because of a strike by conductors in a dispute over pay.
The Rail, Maritime and Transport (RMT) union said its members on TransPennine Express (TPE) were solidly supporting a 24-hour walkout.
More strikes will be held on the next three Sundays.
RMT general secretary Mick Lynch said: “Reports from the ground show that RMT members are solidly supporting the action on TPE this morning in what is a fight for basic pay justice.
“Our members refuse to be treated unfairly and will be continuing with industrial action until the pay discrimination is dealt with.
“The company need to wake up to that fact and we hope today’s action will shake them out of their slumber.”
The company announced an amended timetable for Sunday, with a “significant“ reduction in available services.
“We’re advising customers not to travel on the majority of routes and to plan carefully if journeys are necessary,” said a statement.
