The threat of a strike over jobs by London Underground workers has increased when members of a second union backed a campaign of industrial action.
The Transport Salaried Staffs Association (TSSA) said its members voted by 3-1 in favour of walkouts and by almost 9-1 for action short of a strike.
The Rail Maritime and Transport (RMT) union announced last week that its ballot also showed a big majority in favour of industrial action in protest at plans to cut 800 jobs at London Underground ticket offices.
Both unions have attacked Transport for London (TfL), and London mayor Boris Johnson, over the planned job cuts.
TSSA leader Gerry Doherty will meet RMT general secretary Bob Crow next week to plan a campaign of industrial action, which is likely to start from September 6, the day MPs return to Westminster from their summer break.
An announcement on the strike dates will be made next Tuesday, although the unions will not take any action over the August Bank Holiday weekend, saying they do not want to disrupt the travel plans of families.
Mr Doherty said: "These cuts are being driven by the Government as much as by Boris so our battle is with Downing Street as much as TfL. We want to serve notice on David Cameron that we are not going to sit idly by while he starts cutting jobs and services in London in the run-up to the Olympic Games."
The TSSA said its members voted by 72% in favour of strike action and by 88% for action short of a strike.
A TfL spokesman said: "Safety and customer service are our top priorities and we can assure customers that the Tube's high safety standards will not be affected by the new staffing proposals. We have also committed to achieving the proposed changes without the need for compulsory redundancies.
"Just one in 20 Tube journeys now starts with a ticket office transaction. Under our proposals, staff will remain available at every station to help customers, and all stations that currently have a ticket office service will continue to have one with opening hours that meet customer demand."