Capita IT Services workers are to go on strike over job losses and work being sent to India.
Unite said more than 200 of its members at the computer services firm at four sites in the UK – Reading, Craigforth, Birmingham and Bournemouth – were involved in the dispute.
The union called on Capita to withdraw its offshoring plans.
Unite national officer David Fleming said: "Capita IT staff have voted for industrial action out of anger at Capita's plans to send skilled work abroad.
"Once the skilled jobs are offshored from local communities they never return, which leaves a damaging impact on local economies.
"Unite members are determined to oppose the plan to send their jobs to India and cut other UK jobs, and Unite is calling on Capita's clients to veto the plans."
If talks fail to resolve the row, Unite will agree strike dates and action short of a strike on Thursday.
Unite members voted by four to one for strike action and nine to one for action short of strike on a 65 per cent turnout.
A Capita spokesman said: "In order to maintain its strong position in the marketplace, optimise operational efficiency and continue to enhance service delivery to its clients, Capita's IT services business has concluded that a revised delivery model is necessary.
"Since 30 March 2012, we have been undertaking a consultation process involving employees about a proposal to move limited elements of our work activity to our existing IT services operation in India.
"This consultation process is not yet complete and we are disappointed that 84 employees who are members of Unite – 2 per cent of the entire IT services workforce – have voted in favour of industrial action.
"We have robust processes in place to ensure that this proposed industrial action will not impact our service delivery to clients."