Prison staff have begun protest action after a damning report warned of a "dangerous lack of control" at HMP Bedford, their union said.
Members of the POA, the trade union for prison staff, have been asked to demonstrate outside prisons in England and Wales from 7am "until instructed otherwise".
It follows a report on Thursday from Chief Inspector of Prisons Peter Clarke, who raised the alarm over the potential for a "complete breakdown" in order and discipline at the Bedfordshire prison.
Inmates have effectively taken control at the violent, overcrowded and vermin-infested jail, his report has warned.
POA General Secretary Steve Gillan said the majority of prison officers would be outside prisons in car parks in protest against the "unprecedented decline in health and safety standards over past 6 years".
He told the Press Association: "We are coming out in protest to bring attention, under health and safety legislation, to the Government, to the general public, about conditions in our prisons for both prisoners and my members, of the rise in violence, the rise in drugs, the self-harm and everything that goes with it."
Mr Gillan went on: "Under legislation the Government and employer have a duty of care toward my members, and I'm fed up of hearing of my members receiving smashed eye sockets, broken arms, broken legs, broken jaws, being attacked, spat on, having excrement and urine thrown at them, and enough is enough now.
"We need ministers to start taking control of what's going on."
The POA said about 90 per cent of prison staff were members of the union.
It said it has 20,000 members in England and Wales.