Militant union members of the Ministry of Defence and other government departments will walk out on strike on May 10 in protest over pensions.
Unite said its members are angry over government attacks on their retirement which will force them to work longer and pay more to get less.
Goverment staff voted by 94 per cent to six per cent in a consultative ballot to reject public-sector pension proposals - a similar margin to that of the union's NHS members.
Now the Unite national industrial committee, representing more than 25,000 government employees, such as vehicle maintenance workers, technicians, drivers and storemen, has voted unanimously for strike action.
Unite members will be joining NHS colleagues, as well as members of the 250,000-strong PCS union, representing jobcentre employees and passport control staff, in a nationwide day of action.
Unite general secretary Len McCluskey said: "The emphatic rejection of the proposals by our MoD and government department members makes clear that ministers need to return to the negotiating table for genuine and meaningful talks.
"Unite members in the MoD and the NHS will be joining with other public-sector employees in protest against the fact that the government has continually ridden roughshod over public-sector workers.
"The public sector workforce is being systemically targeted by the right-wing coalition to be the whipping boys for the grotesque failings of the financial elite that have brought this country to its knees economically."
He added: "The dogmatic menu served up by Chancellor George Osborne for the public sector is highly unpalatable - pay freezes set against a backdrop of high inflation, paying more for pensions and large scale downgrading of staff, with regional pay looming.
"Our members have quite rightly concluded we have had enough and they will be making a strong showing on May 10 to register their disgust at the way they have been treated."
Unite MoD/government departments voted 2,440 to reject the pensions' proposals, with 157 to accept, on a 23 per cent turnout.
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