Thousands of prison officers are to be balloted on industrial action, including strikes, in protest at jail privatisation plans, setting them on a potentially damaging collision course with the Government.
Leaders of the Prison Officers Association (POA) announced the move even though it is unlawful for warders to take industrial action.
Around 30,000 POA members in England and Wales will take part in an indicative ballot, which will be considered by the union's executive before the next move is decided.
POA general secretary Steve Gillan said prison officers were "angry" at the Government's privatisation plans for Birmingham and Featherstone 2 in Wolverhampton.
The Ministry of Justice said it was reviewing its contingency arrangements with the police and military in the event of any industrial action.
Justice Secretary Kenneth Clarke revealed last month that troops had been put on stand-by as the Prison Service braced itself for industrial disruption. The POA reacted angrily to news that Birmingham prison and Featherstone 2 are to be run by private security company G4S.
Mr Clarke told MPs: "If people are so unwise as to take industrial action in prisons, the situation can rapidly become far worse than in a normal strike because we start getting disorder among the prisoners."
The POA said last month that it would not make a "knee-jerk" reaction, but decided last week that union members should work only to their contractual obligations, and has now announced a ballot.
Mr Gillan said there would be no recommendation from the POA leaders, adding: "We are just seeking our members' views. The anger is still there and some of our members are now working to contract to show their feelings.
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"The ballot result will determine what we do in the future. It is important to gauge the view of our members through the ballot box, and if it is their will the POA will take clear and decisive action against the privatisation of Birmingham and Featherstone 2."
