Workers from Nortern Rail have launched a 24-hour strike in the bitter dispute over the role of guards.
Members of the Rail, Maritime and Transport union on Arriva Rail North (Northern) were said to be "united and determined".
The strike led the company to reduce services, which had already been affected by the severe weather.
RMT general secretary Mick Cash said; "Our members on both Northern and Merseyrail stand united and determined this morning in these two separate disputes which are about putting public safety before private profit.
"The weather over the past week has rammed home the key point that cutting corners and axing staff in the name of profit on our railways is a dangerous gamble that must be stopped.
"That is the principle that RMT members are standing up for this morning on Northern and Merseyrail.
"We will not accept a situation where guards are hailed as heroes one minute and threatened with the sack the next.
"RMT remains available for talks and it is time for both Northern and Merseyrail to get out of the bunker and start talking seriously about a safe and secure future on our railways."
Northern Rail say they're concentrating on keeping their customers moving.