A rail strike that will affect Sheffield passengers this weekend is 'solidly supported', according to a union.
Members of the Rail, Maritime and Transport union working on Arriva Rail North trains began a three-day walkout today.
Although the operator expects more than 40 per cent of services to run, with rail replacement buses also in place, those travelling across South Yorkshire are likely to face delays.
Guards working for Merseyrail will also strike today and on Monday.
RMT general secretary Mick Cash said: "Once again RMT members are standing firm in the fight for safe and accessible rail services.
"The action in the two separate disputes on Northern and Merseyrail is being solidly supported across all routes in the battle for safe railways for all.
"Despite relentless campaigns of threats and intimidation RMT members are out on the picket lines this morning putting the basic principle of rail safety before the profits of the rogue rail operating companies.
"Both Northern and Merseyrail should get out of the bunker, stop doing the bidding of their political masters and start talking seriously with the union about a safe and secure future that guarantees the role of the guard on their trains."
Today and on Monday the majority of Northern services will run from 7am to 7pm, though many routes will start to wind down from late afternoon.
On Sunday, most services will operate from 9am to 5pm.
Northern regional director Sharon Keith said: "We are doing everything we can to keep our customers on the move during the three days of industrial action affecting our network.
"We will be running more than 40 per cent of our usual services, but those trains that do run will be on an amended timetable and are likely to be extremely busy.
"We ask our customers to plan carefully, allow extra time for travel, and to consider whether their journeys are necessary."
This is the fourth strike in the dispute at Arriva North, which operates Northern rail services. The last planned strike on May 30 was cancelled because of the terror attack in Manchester.
The union claims Arriva Rail North 'continues to resist all efforts to make progress in the long-running dispute over rail safety and the head-long dash towards driver-only operation'.
The dispute centres round the train driver rather than the conductor opening and closing the doors and dispatching the train from a station.
Driver-only trains were first introduced in the UK in 1982, and now makes up around 30 per cent of the UK mainline network, as well as London Underground.
The Rail Safety and Standards Board and the independent regulator, the Office of Rail and Road have both concluded that driver-only is safe - but the unions have disputed the findings.
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