The last strike resulted in major disruption across London Millions of Londoners face disruption as Tube staff prepare to start a 24-hour strike in protest at plans to reduce ticket office staffing.
The strike – the second in recent months – begins at 1830 BST.
The RMT and TSSA unions are angry at plans to cut 800 jobs, which they say will affect safety.
Transport for London (TfL), which has pleaded with the unions to call off the “pointless” strike, says change to the network is unavoidable.
The organisation is putting on 100 extra buses and increasing capacity for river journeys to deal with the strike.
The last strike led to travel chaos across the capital.
RMT has instructed all its members to walk out from 1829 BST and has banned them from accepting any overtime.
RMT general secretary Bob Crow said: “We have warned repeatedly that TfL’s cuts plans are playing fast and loose with safety and will turn the Tube into a death trap.
“We remain available for talks but the current cuts to jobs and safety must be halted before we have a tragedy on our hands.
“We have no choice but to take action on behalf of Londoners who depend daily on a safe transport system.”
Mike Brown, managing director of London Underground, said: “In refusing to talk to us for nearly a week, and demanding we withdraw all proposals for staffing changes before talks could progress, the leadership of the RMT and TSSA have seemed intent on disruption.
“But changing London Underground is not a choice, it is essential, and we will not be diverted from moving with the times.
“The leaderships have tried to scaremonger, citing safety issues, but they did not put a single safety-related issue to us during talks, nor have they responded to our request that they set out their specific safety concerns.”
The strike can be followed on a BBC London Twitter feed and a live update web page.
An interactive map will be produced showing areas on the network with severe disruption.
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