Prison staff say they are "being used like punch bags" after a prosecution against a prisoner who allegedly broke a female officer's jaw was dropped.
The officer was injured at Moorland prison in Doncaster during riots in November.
The Prison Officers Association (POA) has made a complaint about the Crown Prosecution Service (CPS) decision to drop the case.
The CPS said it will investigate the complaint.
Members of the POA gathered in London earlier to debate serious safety concerns across the prison service, which they say are being ignored.
Rick Midgley, POA branch secretary at Moorland prison, said the dropping of the case against the inmate "just leaves you feeling that nobody cares".
He said cuts to the service are leaving officers at risk, adding: "It's like open season.
"If they keep taking staff off us prisons will be less safe.
"It's a downward spiral and it's asking for trouble."
Colin Moses, National Chairman of the POA, said: "It is clear that the health and safety of people in prisons is being ignored and my members are being used as cheap punch bags for prisoners as this government pushes through dangerous and unsafe staffing levels and regimes in an attempt to save money."
It emerged earlier this month that soldiers and RAF personnel are being trained to move in to control prisons in case prison officers take industrial action.
The Ministry of Justice said it had contingency plans in place for every possible eventuality.