The three-day walkout by members of the RMT union has led to Northern Rail running a skeleton service on its routes across the region.
The company has warned commuters to expect disruption and has said all services its services are "extremely busy".
While the majority of Northern services are running between 7am and 7pm today, many routes will reduce in frequency and "wind down" from late afternoon.
In a statement, Northern Rail said: "All services are expected to be extremely busy. Please allow extra time for journeys, plan carefully and consider whether travel is necessary."
The three days of industrial action is being led by members of the RMT union started on Saturday and affected services across the weekend.
RMT general secretary Mick Cash said the dispute is about "putting safe rail travel before private profit."
For the full updated timetable visit: www.northernrailway.co.uk/industrial-action