London Underground workers have voted to go on strike over controversial plans to close Tube ticket offices.
Members of the Rail Maritime and Transport union backed walkouts by 77%, and other forms of industrial action by a bigger margin, threatening industrial action in the coming weeks.
The union's executive will now consider the vote, and will have to give seven days notice of any stoppages.
Members of the Transport Salaried Staffs Association will also vote in the coming weeks on whether to launch a campaign of action in protest at the closure of all 260 Tube ticket offices, with the loss of hundreds of jobs.
Any industrial action is likely to be co-ordinated between the two unions.
RMT general secretary Bob Crow said: "RMT members on London Underground have voted by a massive majority for both strike action and action short of a strike in a dispute which is wholly about cash-led cuts plans that would see the axing of nearly 1,000 safety-critical jobs and the closure of ticket offices at a time when the Tube network is under growing pressure from customer demand and needs more staff and not less to ensure safe and efficient operation.
"Not only are 1,000 posts on the line but staff remaining are going to be forced through the humiliating and degrading experience of re-applying for their own jobs - the same staff who have been hailed as heroes when the Tube has faced emergency situations.
"That is a kick in the teeth for the loyal and experienced Tube workforce who have kept services running safely and efficiently under constant pressure from weight of demand and a creaking and under-resourced infrastructure.
"These cuts would hit the vulnerable, the elderly, those with disabilities and women the hardest. De-staffing stations, with supervisors running operations three stops down the line on an iPad would turn the Tube system into a criminals' paradise where those with violence and robbery on their minds are given a clear run.
"RMT will work with our sister unions and passenger groups to ensure that Tube users understand just what's at stake as (London mayor) Boris Johnson turns his opportunist election pledges on their head.
"Before the Tories start shouting the odds, they should take note of the fact that the turn-out in this ballot was higher than the last mayoral and GLA elections and the vote in favour massively outstrips anything that those same politicians can even dream of in terms of a popular mandate."
TSSA general secretary Manuel Cortes blamed the ballot on the "reckless" behaviour of Mr Johnson, who he said was refusing to meet the unions over their genuine fears for safety and security.
He said: "It was the mayor who came into office in 2008 with a firm pledge to keep open every ticket office on the grounds of keeping passengers safe and secure at all times.
"Now he wants to scrap the lot, claiming there will be no problems because he will keep staff on station platforms - those that keep their jobs, that is."
Transport for London said sales at ticket offices accounted for only around 3% of all journeys, after announcing that staff would be switched to station concourses.