London Underground strike to cause travel disruption
Tube passengers face disruption to their journeys when a third strike in a dispute over jobs begins on Tuesday.
Members of the Transport Salaried Staffs' Association (TSSA) and Rail Maritime and Transport (RMT) union are protesting at planned job cuts.
Maintenance workers are due to walk out at 1900 GMT with other workers joining them at 2100 GMT.
Transport for London (TfL) says cuts will have no impact on safety and will not result in compulsory redundancies.
Union members are opposed to the axing of 800 jobs affecting station managers and ticket office staff.
More than 11,000 union members are expected to take part in the action, with engineering staff striking from 1900 GMT and operational staff not booking on for shifts scheduled to start from 2100 GMT.
RMT general secretary Bob Crow said: "All we have been asking is that the London mayor stick to the pledge he made during his election campaign, when he too recognised that people wanted to see stations staffed properly.
"The message is simple: suspend these cuts and we will suspend our action."
Pledging to keep Londoners moving during the stoppage, Transport for London (TfL) has laid on extra bus and river services.
During the last strike on 3 October TfL said London Underground operated 40% of services.
London mayor Boris Johnson said: "Londoners have shown that they will not be deterred from their daily business by these pointless strikes.
"I hope the RMT and TSSA leaderships will face facts and see that their action achieves nothing aside from depriving their members of another day's pay."
A fourth strike is planned for 29 November.