Workers at three rail companies are said to be "solidly supporting" strikes taking place today amid bitter rows over staffing and driver-only trains.
Members of the Rail, Maritime and Transport union (RMT) at Merseyrail, Arriva Trains North and Southern walked out for 24 hours, with little sign of a breakthrough in the disputes spreading across the industry.
Picket lines were mounted outside stations, with the action causing disruption for passengers including racegoers attending the Grand National.
The action being taken by staff at Arriva Trains North is affecting Northern trains, with the company expecting run around a third of its usual services.
Mick Cash, general secretary of the RMT, said: "Support for all three strikes today is rock solid, with pickets out in force and morale high as our members on Southern, Northern and Merseyrail continue the fight for rail safety.
"It is down to all three companies to now get round the table with union negotiators and reach settlements based on the guarantee of a guard and a safe railway for all."
The strike at Arriva and Merseyrail coincides with the Grand National at Aintree, the biggest horse race of the year, which is attended by tens of thousands of people, many travelling by train.
Merseyrail was expecting drivers in the Aslef union to refuse to cross RMT picket lines, so a team of managers ias being drafted in to provide a service before and after the race between Liverpool city centre and Aintree.
There will be a seven-and-a-half minute service at "key" times, but fewer or no trains on other parts of the network.
Rail replacement buses will run on some lines.
Jan Chaudhry-van der Velde, managing director of Merseyrail, said: "Despite the RMT's best efforts to scupper this iconic event and create misery for the tens of thousands of people who look forward to it all year, we've developed a timetable aimed at getting as many people between central Liverpool and Aintree as we normally do on Grand National day."
Arriva Trains North, which trades as Northern, said its services will be "significantly" reduced, with the last trains leaving Liverpool Lime Street between 7.02pm and 8.16pm.
It plans to run more than 850 services today, with the majority running between 9am and 5pm.
The Merseyrail and Arriva disputes are over new trains coming into service in 2020 which will be driver-only, while the Southern row is now a year old, with the RMT taking its 31st day of strike action today.
The union paraded an advertising billboard through Liverpool and Aintree explaining why the RMT is taking strike action to defend safety-critical guards.
Southern said it expected to run most of its trains despite the strike.