London Underground maintenance staff will stage a series of 12- and 24-hour strikes in a dispute over track safety concerns.
The Rail, Maritime and Transport (RMT) union said its members will walk out at 6.30am on 12 February for 24 hours, with seven further strikes planned until June.
Commuters are being warned to prepare for more disruption ahead of a 48-hour walk out this weekend.
Station staff are due to strike from 9pm on Saturday, 6 February, over a dispute concerning the closure of ticket offices and changes to work rosters under the "Fit for the Future" scheme.
A page on Transport for London's website says: "The Tube strike affects station staff, and the impact is difficult to predict in advance.
"We will open whichever stations we can, based on the staff who sign on to their shifts. Please allow more time for your journey on these days.
"As staff shifts change over the course of the day on Sunday and Monday, some stations may only open in either the morning or the afternoon."
RMT said the latest series of strikes involved 1,500 of its staff in a row over "basic safety issues".
Mick Cash, RMT general secretary, said: "Nobody should dare to under-estimate the severe impact on track safety that the changes bulldozed through by London Underground have unleashed and which have forced our members to take a prolonged period of industrial action to protect both themselves and their colleagues.
"From a situation where everyone knew how to access the track, we now have anarchy and uncertainty.
"Into this mix we have engineering train movements that we believe will lead to someone being killed and this union will not sit back and wait for a disaster to happen."
London Underground's Steve Griffiths said: "Safety is always our top priority and we have robust and comprehensive procedures in place to ensure that any staff working on the track are kept safe and are aware of any train movements.
"We have talked to our trade unions extensively about the changes we have made to track access for engineering work and will continue these discussions next week."
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