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.
"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.
"We will continue to hold weekly lunchtime protest meetings and persuade our members to follow the policies of the union."
POA chairman Colin Moses said: "It is vital that the members have their say through the ballot box and decide what course of action they are prepared to take to support their colleagues, who have been sold off to the private sector.
"Prisons should not be run for profit and whilst Ken Clarke took great pride in announcing the privatisation of these prisons, the POA remains of the view that it is the state's responsibility to imprison its citizens and not profiteers."
A Ministry of Justice spokesman said: "Our aim is to avoid any form of industrial action and we will continue to talk to all unions to do everything possible to achieve that.
"However, given the risks and complexities involved in running prisons, it is sensible and appropriate to review our contingency plans for dealing with widespread industrial action.
"There was a previous trilateral agreement with the police and the military for the provision of support to prisons and we are currently reviewing those arrangements and working with the MoD and police to ensure that our contingency arrangements are as strong as possible."
Eoin McLennan, president of the Prison Governors Association said he did not believe POA members would support industrial action.
"Industrial action would be illegal and prison officers could be held personally liable. Also in the current economic climate it might be difficult for them to find other employment, so I don't expect them to support action. I hope common sense will prevail."Reuse content