STORY: Britain faces its biggest rail strike in 30 years.
More than 40,000 workers are due to walk out on Tuesday (June 21), Thursday (June 23) and Saturday (June 25) to protest pay and job cuts.
Picket lines formed at dawn Tuesday, bringing the network largely to a standstill.
London's Underground was also mostly closed due to a separate strike.
Prime Minister Boris Johnson said the action would hurt businesses as they try to recover from the health crisis.
But unions have said rail strikes could be one part of a so-called 'summer of discontent'.
They argue teachers, medics and more key workers could take industrial action as inflation pushes towards 10%.
Opposition lawmakers have also criticised the government for not getting involved in talks to settle the dispute.
Ministers claim it is a matter for the unions to work out directly with rail employers.
Britain's economy rebounded strongly from the health crisis at first.
But a combination of factors including labor shortages, supply chain disruption and post-Brexit trade problems have led some economists to warn of a recession.