Prison officers across England and Wales have voted for possible strike action unless their continued demand for a pay increase is met.
Their union, the Prison Officers' Association (POA), said that the moral of wardens was at "rock bottom" with "prisons bursting at the seams".
Its members are furious that a recommendation by an independent review board to award officers a 2.5% pay rise in April was turned down by the government.
Instead, Whitehall gave the go-ahead for a below-inflation increase of 1.9%.
"The morale of staff throughout England and Wales is at rock bottom," said Colin Moses, national chairman of the POA.
"The level of assaults against staff has risen to more than eight a day and in turn the prisoner to staff ratio has also risen."
He said prisons had become more dangerous places to work and urged the government to take action to restore the members' confidence in their employer.
At the POA's annual conference in May, its 28,000 members were balloted on whether they would consider strike action to resolve the pay dispute.
The vote came following the second successive year in which prison officers received a below-inflation pay rise. Last year, wardens were awarded a 1.4% increase.
"At our conference in May our membership was absolutely incensed," Mr Moses said.
"We took a ballot to ask whether they would be prepared to take industrial action, up to and including strike action. Eighty per cent of the ballot papers returned said they were.
"There are now close to 81,000 prisoners within our prisons and officers are facing an increase in the rate of violence towards them.
"We are professional enough to deal with that if we are given the correct resources, but there have been year on year cuts by the government in the budget for prisons."
The POA will now consider the result of the ballot at the national executive committee meeting next week.
Under its contract with government, the union is currently legally obliged not to undertake any industrial action that would disrupt the HM Prison Service.
However, the union has given notice to withdraw from that contract allowing them the potential to strike.
A spokeswoman for the Ministry of Justice said: "Pay rises for those at the top end of their pay scales have been below inflation for two years.
"But those still rising on the incremental pay scales are receiving above inflation rises.
"Prison officers work in an extremely difficult environment with some of the most difficult people in society. Despite an increasing population there is no evidence of an increase in the rate of assaults on staff."