The RMT has announced another strike on Saturday - with Northern services in Sheffield and Doncaster once again being targeted.
A Northern spokesman said: "The majority of available trains will operate between 7am and 7pm as we focus on running as many trains as we can to get you into work and home again.
"During these hours, we plan to operate around 45% of the normal Saturday timetable.
"As the overall number of trains running will be reduced, we expect trains and any replacement buses we operate to be extremely busy. Please allow extra time for journeys, plan carefully and consider whether travel is necessary."
The services are dependent on weather and many Northern routes have already been badly hit by this week's severe weather conditions.
A statement added: "During the RMT strike action we expect all services to be busy, especially in the morning and evening peak periods, and advise you to allow extra time to travel."
Full timetables are available HEREPassengers have been told they may be able to use tickets on other train operator services.
You will be able to use tickets on Arriva Bus services (including Yorkshire Tiger) to make journeys you would otherwise have made by rail.
The following operators will accept these tickets: Arriva Trains Wales, Cross Country, East Midland Trains, TransPennine Express, Grand Central, Hull Trains, Virgin Trains East Coast and Virgin Trains West Coast. Customers are advised to travel as close as possible to the original booked train times on these days.