The Government has won its High Court bid to obtain a permanent ban on industrial action by prison officers.
The Ministry of Justice's application followed a move in February by the POA - the Professional Trades Union for Prison, Correctional and Secure Psychiatric Workers - to call on its members to take action short of a strike.
That led to an interim injunction requiring the POA to withdraw a circular instructing members to refuse to undertake certain voluntary tasks.
Daniel Stilitz QC said earlier this month that the case was brought "to ensure that POA does not seek to breach the law again".
John Hendy QC, for the POA, said each of the activities referred to in the circular were voluntary in nature and there was no evidence that any of the 35,000 members had been asked to disobey any lawful instruction.
He said steps were taken to ensure members fully complied with the February order and the court was being asked to consider the lawfulness of a circular which was no longer extant and never implemented.
On Wednesday in London, Mr Justice Jay said the Ministry of Justice was entitled to a final injunction.
Mr Stilitz said that, in view of the importance of maintaining discipline and security within the prison service, Parliament had enacted a prohibition on inducing prison officers to take industrial action under the Criminal Justice and Public Order Act 1994.
Despite this, he added, the POA had recently called or threatened to call industrial action on a number of occasions.
"Any inducement which leads prison officers to cease to provide services which they otherwise would have done is unlawful."
The history of "unlawful" industrial action, together with the "inflammatory rhetoric"used by the POA, suggested a continuing willingness to call for industrial action despite Parliament having "clearly and deliberately" outlawed it.
"The Secretary of State is concerned that, unless the position is determined definitively by the court, there will be renewed calls for unlawful industrial action in the future.
"It is therefore critical to safeguarding the proper and safe functioning of the prison service that the scope of the statutory prohibition is confirmed."
The judge said: "The POA has lost not just on the facts - the wording of the circular, and the finding that the circular was likely to generate a risk to the safety of prisoners and staff - but also on the important point of principle."
The POA said later that it had instructed its legal advisers to seek leave to appeal against the decision.
General secretary Steve Gillan said: "I suppose one day the Prison Service and Government will be dragged kicking and screaming into a modern era of employee relations rather than hiding behind restrictive anti-union laws such as Section 127 of the Criminal Justice Public Act 1994."
He added: "The health and safety of our members and those we look after are vitally important and the Prison Service and Government cannot hide behind the courts forever.
"The POA will continue to support our members with health and safety legislation and will expose the hierarchy of the Prison Service and Government on their continued failures.
"Perhaps it is now time for some directors in the Prison Service to step aside or indeed be removed from their positions.
"Their failings are blatantly obvious for all to see."
A Prison Service spokesman said: "We fully share the POA objectives to make prisons safe and decent places where frontline staff are recognised and rewarded for the challenging work they do.
"Unlawful industrial action is not the way to achieve that aim.
"We are committed to building on the essential reforms that are already under way to make prisons places of safety and reform.
"We are investing £100 million a year to recruit an extra 2,500 frontline prison officers.
"The most recent figures show the number of prison officers in post has increased by 515 compared with the previous quarter, meaning we are on track to delivering this important commitment."