Workers who maintain and upgrade Tube lines on London Underground have voted to go on strike in a dispute over pensions and benefits.
The Rail, Maritime and Transport union (RMT), which represents around 1,000 staff on the Tube Lines contracts, said its members backed walkouts by 4-1.
The staff work on the Piccadilly, Northern and Jubilee lines and provide a number of services, including emergency repairs, across the entire network.
The row is over union demands for all Tube Lines staff to be allowed to join the Transport for London pension scheme and receive the same travel concessions as those who work for London Underground.
The RMT executive will now consider the next move, including whether to set strike dates, which officials said would cause "widespread disruption".
RMT general secretary Bob Crow said: "This is a massive mandate for action following a straightforward demand for parity with other Tube staff.
"This dispute is about justice and about ensuring that all groups of staff under the umbrella of London Underground receive the same rights and benefits.
"We have gone through all the negotiating channels on both these issues but Tube Lines has refused to budge and have refused to engage in meaningful talks and that pig-headed approach has raised the temperature on the shop floor and is reflected in this result."
The RMT former Metronet employees have been allowed back into the TfL Pension Fund so they now have the same travel facilities as other LU employees.
Mr Crow added: "Tube Lines is now a wholly owned subsidiary of Transport for London and there is simply no excuse for refusing to give equal pension and pass rights.
"The union remains ready to talk, and this strong mandate for industrial action shows Tube Lines and TfL the depth of anger there is over this blatant lack of fairness and justice."
Lee Jones, operations director for Tube Lines, said: "We note that the outcome of the RMT's ballot showed that less than 44% of its members voted in favour of strike action.
"We have been discussing this issue with our trade unions for some time, and we will continue to try to find a way forward through constructive discussion."