Tube workers are set to stage 48-hour strike next week over a long-running dispute over Tube ticket office closures.
Members of the Rail, Maritime and Transport union have been instructed not to book on for any shifts between 2100 hrs on October 14 and 2059 hrs on October 16.
The walkout threatens travel disruption in the capital and coincides with strikes by council workers and civil servants across the country in separate disputes over pay, jobs and cuts.
The latest phase of action in RMT's Every Job Matters campaign follows a mass meeting of reps to report back from talks with London Underground.
The union said that although some limited progress has been made its executive has taken the view that it is not enough after months of negotiations and that the only option is to move back into a further round of strike action.
RMT general secretary Mick Cash said: "RMT negotiators have made every effort in the long-running talks to resolve a range of issues that impact on our members jobs, their pay and working conditions and the safety of the services that they provide to the travelling public.
"The cuts, currently being bulldozed through, would de-staff whole areas of the Tube system at a time of surging passenger demand and would make evacuation and other basic safety procedures a physical impossibility.
"The axing of ticket offices and station staffing grades would render the Tube a no-go zone for many people with disabilities and for women travelling alone. The cuts ignore the realities of life that we saw when services broke down last week and the recent surveys which point to an increase in violence and sexual assaults.
"RMT will not stand back and allow Government-driven austerity cuts to hollow out the Tube system and leave it as a dangerous shell. We are also fully aware that the current cuts are just part of a multi-billion pound attack that will include such lethal ideas as driverless-operation.
"The strike action next week is designed to force the mayor to instruct his senior officials to back away from this toxic cuts package and engage in serious and meaningful negotiations."
Unions have been campaigning against plans to close ticket offices since they were unveiled last year.
LU say few tickets are bought at offices now, arguing that staff would be better used by being stationed on concourses.