Strikes by rail workers today were expected to bring train services to a halt across the country in the latest disruption caused by a wave of industrial action.
Teachers in England and university staff will also continue their walkout from Wednesday, when they took part in one of the single biggest days of action in a decade.
Up to half a million teachers, lecturers, junior doctors, civil servants, London Underground drivers, BBC journalists and Amazon employees went on strike on budget day.
Today members of the Rail, Maritime and Transport union (RMT) at 14 operators were due to walk out in a long-running row over pay, jobs and conditions.
Passengers were warned to expect disruption throughout the day, and again on future strike dates this coming Saturday, as well as Thursday 30 March and Saturday 1 April.
It was expected 40-50% of train services will run nationally, but there were due to be wide variations across the network with no services at all in some areas.
Trains that were due to run were expected to start later and finish much earlier than usual, typically between 7.30am and 6.30pm.
Services on Friday morning could also be disrupted because much of the rolling stock will not be in the right depots.
Steve Montgomery, who chairs the Rail Delivery Group, said: "This latest round of strikes will be a further inconvenience to our customers, who have already experienced months of disruption, and cost our people even more money at a time they can least afford it.
"They will also be asking why the RMT leadership blocked the chance to resolve this dispute by refusing to give their members - many of whom would have benefited from a 13% increase - a say on their own deal.
"Unfortunately, while we will pull out all the stops to keep as many trains running as possible, there will be reduced services across many parts of the rail network on all four strike days, so our advice is to check before you travel."
A Department for Transport spokesperson said: "RMT members at train operating companies are being denied a say on their own future, while being forced to lose more pay through avoidable strike action.
"We urge the RMT's executive to put the Rail Delivery Group's very fair offer to a democratic vote of their members, like it has on two separate occasions for RMT members working for Network Rail."
RMT general secretary Mick Lynch said: "Rail employers are not being given a fresh mandate by the government to offer our members a new deal on pay, conditions and job security.
"Therefore, our members will now take sustained and targeted industrial action over the next few months.
"The government can settle this dispute easily by unshackling the rail companies.
"However, its stubborn refusal to do so will now mean more strike action across the railway network and a very disruptive overtime ban.
"Ministers cannot continue to sit on their hands hoping this dispute will go away as our members are fully prepared to fight tooth and nail for a negotiated settlement in the months ahead."