Prison officers have threatened to launch fresh industrial action over a row about wearing union badges.
Officers walked out in the summer over a staged 2.5% pay rise
Union leaders say some officers wearing the badges, made to mark a wildcat strike in August over pay, have been threatened with disciplinary action.
The Prison Officers' Association (POA) says if any member is disciplined over the issue, it will call new strikes.
But the Prison Service says the badges commemorate "an unlawful act" and are "incompatible" with an officer's role.
Thousands of prison staff in England and Wales walked out in August over the government's decision to give public sector workers a 2.5% pay rise in two separate stages.
The badge marks the wildcat action in August
At the time, the Ministry of Justice said the strike had "an immense impact" on the operation of the prison service, leading to cancelled court appearances and prisoner transfers, and disturbances at a young offenders institute.
The government also said the POA had reneged on a voluntary ban on industrial action within the service and Justice Secretary Jack Straw said he was "actively considering" banning strikes.
Now the POA's chairman, Colin Moses, has warned a second wave of strikes could take place over the issue of wearing the union badges, which members sell for £1 for charity.
"My members are being assaulted on a daily basis. Prisoners are being transferred from prison to prison, the public are being placed at risk as unsuitable prisoners are being sent to open jails as the service try to cope with the current crisis," he said.
"But, what is the director general concerned about? Staff wearing badges."
The union's general secretary, Brian Caton, accused the Prison Service of "engineering a dispute, so that they can ask the courts to shackle the POA".
"The Prison Service is in crisis and morale amongst prison staff is at an all time low," he added.
A Prison Service spokesman said the job of prison officers was to "uphold the law".
"This badge commemorates an unlawful act and is therefore incompatible with their role."
The spokesman said rules made it clear that staff could only wear one badge from an officially recognised trade union and they prohibited wearing badges for "most other areas including clubs and societies and political badges".
He added that legal advice was that the rules were clear and they stated that "the wearing of badges is at management discretion and we have the authority to stop POA members wearing such badges whilst at work".
"The Prison Service is advising governors not to allow POA members to wear such badges whilst on duty."