Prison officers have been ordered back to work after thousands joined a protest on Tuesday held amid claims jails are "in meltdown".
The government took the unusual step of launching a High Court bid to block industrial action after guards gathered outside establishments around the country.
What has happened?
Thousands of staff have stopped work after the Prison Officers Association directed its members to take protest action after talks with the government over health and safety issues broke down.
Why have they taken this step?
The POA said surges in violence and self-harm, along with recent incidents including an alleged murder and the escape of two inmates, show the service is "in meltdown".
What has the government said?
The Ministry of Justice said there is no justification for the action, which it described as "unlawful", and pledged to take the matter to the courts.
How bad is the situation in jails?
Rising levels of violence have prompted a flurry of warnings about the state of prisons, with assaults on staff up by 43% in the year to June.
What are the reasons for the problems?
Union bosses have highlighted dwindling staffing numbers, while the availability of drugs - previously known as legal highs - have been identified as a major problem.
Campaign groups have called for prison numbers to be lowered to reduce overcrowding.
What is the government doing about it?
Justice Secretary Liz Truss, who has condemned "unacceptable" levels of violence in prisons, unveiled her blueprint for prison reform earlier this month.
It includes a recruitment drive to add 2,500 new officers to the front line and "no-fly zones" to stop drones dropping drugs and other contraband into prisons.