More than 50,000 workers will take part in a three-day national strike next week after talks over pay freezes and job cuts failed.
Britain's biggest strike action on the railway network in over 30 years will go ahead, after talks over pay broke down.
Rail Maritime and Transport Workers union's general-secretary Mick Lynch said on Saturday there had been discussions in recent weeks with rail infrastructure body Network Rail, train companies and London Underground.
But he added that "no viable settlements" were found.
The failure of talks means more than 50,000 workers will take part in a three-day national strike on Tuesday, Thursday and Saturday next week.
London Underground workers will also stage a 24-hour walk-out on Tuesday.
The action coincides with major events including the Glastonbury music festival, as well as national exams for teenagers.
Major disruption is predicted but the RMT defended the industrial action and blamed the Conservative government for cutting billions of pounds (dollars, euros) in funding from the transport network.
Jobs had been lost across the sector, while wages for staff that remain were failing to keep pace with soaring inflation, which is at a 40-year high, it argued.
"In the face of this massive attack on our people the RMT cannot be passive," said Lynch.
"So... we are confirming that the strike action scheduled to take place on 21st, 23rd and 25th June will go ahead."
The Rail Delivery Group, an industry body for passenger and freight operators, predicted that "millions of people" would be affected.
It promised to try to keep as many services running as possible but warned that "significant disruption will be inevitable and some parts of the network will not have a service".
The strikes, which the RMT said are the biggest since 1989, will likely compound travel chaos, after airlines were forced to cut flights due to staff shortages, causing delays and frustration.
The Department for Transport said the RMT's decision was "hugely disappointing and premature" and warned that jobs could be at risk if passengers turn away from rail, just as the sector tries to recover from a slump during the pandemic.
"We urge the RMT to reconsider so we can find a solution that delivers for workers, passengers and taxpayers alike," a spokesman said.