Thousands of workers on the London Underground are to begin the first in a series of 24-hour strikes on 6 September in a row over 800 job cuts.
The Rail Maritime and Transport (RMT) union and Transport Salaried Staffs Association (TSSA) said walkouts would then be staged on a monthly basis.
The unions said they would continue striking until plans to reduce ticket office opening hours were withdrawn.
London Underground (LU) said there would be no compulsory redundancies.
The unions said up to 10,000 members would take part in the industrial action.
Maintenance and engineering staff will walk out for 24 hours at 1700 on 6 September, 3 October, 2 November and 28 November.
Other workers, including Tube drivers, signallers and station staff, will strike for 24 hours from 2100 on the same dates.
An indefinite overtime ban for Tube staff belonging to both unions will also start at a minute after midnight on 6 September.
RMT general secretary Bob Crow said the cuts were unacceptable and would undermine safety and the service for passengers.
He said: "The mayor was elected on a promise of maintaining safe staffing levels and he is doing the opposite, planning to leave stations and platforms dangerously understaffed and threatening to turn the network into a mugger's paradise."
TSSA general secretary Gerry Doherty said: "Boris Johnson may be prepared to go into the Olympic Games with a second class Tube service when the eyes of the world will be on the capital - we are not.
"We will defend a vital public service on which millions of people depend every day of their working lives.
"We will not see jobs and services sacrificed to pay for the sins of the City of London and Wall Street."
'Bad for London'
Howard Collins, LU's chief operating officer, said the cuts were needed because some ticket offices sold fewer than 10 tickets an hour.
Transport Secretary Philip Hammond said the strike would be "bad for London".
He said: "At a time when public finances are under pressure, any strike by Tube workers will be seriously damaging - undermining the case we are making within the spending review for continued investment in the Tube."
The London Chamber of Commerce has estimated the cost of the strikes to the capital would be £48m a day.