Northern rail staff are set to go on strike tomorrow - affecting train services in Sheffield and further afield.
The Rail, Maritime and Transport union (RMT) said its members will walk out for 24 hours in a row over the future role of train guards.
The train operator runs services from Doncaster to destinations including Sheffield, Leeds, Scunthorpe and Hull.
Tomorrow's strike action is also expected to cause problems on the roads as commuters take their cars to work instead.
Northern Rail bosses estimate 40 per cent of train services will be able to run, but there could be long delays.
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Mick Cash, RMT general secretary, said the industrial action was the result of Northern bosses failing to guarantee the future role of guards on trains.
When is the strike happening?
Northern Rail's train drivers and guards will walk out on strike between 12.01am and 11.59pm on Monday.
Why are they taking strike action?
Rail bosses want drivers to open and shut the train doors when stationary on a platform. At present, train guards do this. Unions have said the proposals are 'unsafe'.
RMT general secretary Mick Cash said: members have voted by a 'massive majority' for both strike action and action short of a strike on Arriva Rail North in a dispute which is all about 'putting public safety before private profit'.
Will my service be affected?
Northern Rail has said it can run less than half of the services on a normal day. Train bosses have laid on around 300 rail replacement buses to those services affected.
Regional director Sharon Keith said: “Earlier this week we announced we would be able to run approximately 980 rail services on the day of the industrial action. After further planning we will also be able to operate around 300 extra rail replacement buses.
“We expect all services, rail and bus, to be extremely busy and ask for customers’ patience on Monday. We would also ask customers to take time to consider whether journeys are necessary and, if they are, to plan carefully.
“As with the rail timetable, we have focused our planning efforts on providing a service between 7am and 7pm. And we have sought to provide an additional transport option for customers on the busiest routes that did not benefit from a rail service in the revised timetable.”