Transport for London said that all lines will be badly hit from Tuesday to Friday with “significantly reduced” numbers of trains at best. On some lines there may be no services at all at times.
The first of two separate planned 24 hour walkouts is due to start on Tuesday at noon and run until one minute before noon on Wednesday.
The second will begin at noon on Thursday and run until one minute before noon on Friday.
Tfl said the timing of the strikes meant that “morning service are likely to be closer to normal on Tuesday and Thursday while the evening service will be more comprehensive on Wednesday and Friday”.
It advised passengers to complete journeys on the Tube by 1pm on Tuesday and Thursday.
The dispute is over rostering arrangements made to preserve a regular Underground service as a normal timetable is restored – including the Night Tube - after the pandemic.
This week ridership reached 51 per cent of pre-Covid levels, the highest since the start of the pandemic, and is expected to climb further after the school holidays.
Nick Dent, director of customer operations for London Underground, said: “We have made changes to the way we roster drivers to help us provide a regular Tube service. They have also helped to create more flexibility for many of our drivers and have resulted in no job losses. We have been able to return the Waterloo & City line to service as a result of these changes, and they will help as we continue to work on fully restoring other parts of the Tube service.
“Our drivers have been vital in keeping the Tube running during the pandemic, ensuring that key workers could move around the city during the lockdowns and helping fuel London’s recovery in more recent weeks.
“This new arrangement means that all drivers have been given the opportunity for full-time work and long-term job certainty, while Londoners can continue to rely on the regularity of Tube services.
“I urge the RMT to withdraw this action and to continue engaging with the constructive discussions we have been having in recent weeks so that we can avoid this unnecessary disruption to Londoners going about their daily lives.”