Workers at one of the country's biggest rail operators are staging their 35th strike in a long-running dispute to axe guards on trains.
Members of the Rail, Maritime and Transport union (RMT) on Arriva Rail North (Northern) are striking for 24 hours.
Northern said it expected to run fewer than a third of its services, with replacement buses on some routes.
The union claims imposing driver-only services is a risk to public safety.
The union has held Saturday strikes at Northern since the end of August, a pattern it will continue until the end of the year.
Northern said it was operating a reduced timetable with very few trains running after 18:00 GMT.
'Eyes and ears'
Passengers were advised to "plan carefully" if they intended to travel on the rail network.
Barrow-in-Furness MP John Woodcock tweeted earlier this week he had received a letter from Home Office minister Ben Wallace detailing his worries about removing guards.
Mr Woodcock, an independent MP, tweeted: "Home Office believes axing train guards could undermine fight against county lines drugs trade - big step in the campaign to keep them."
RMT general secretary Mick Cash said: "The guards on our trains are the eyes and ears of the rail service and play a crucial role in combating crime, whether that's assaults, sexual harassment or spotting those who may be in a vulnerable position like young kids being used as mules by county lines drug gangs.
"This ministerial letter backs up everything the RMT has been saying."