NSW prison officers fear for their safety due to overcrowding and reduced staffing numbers in the state's jails.
The prison population is close to 11,000 inmates - the highest prison population figure on record - and prison officers are refusing to take any more.
Officers are also campaigning for workers' compensation entitlements to be restored after the system was reformed in 2012 by the state government.
Public Service Association of NSW (PSA) Steve Turner says overcrowding is making the situation even more dangerous.
"This overcrowding is putting a lot of pressure on (prison officers). You might see as little as 20 prison officers looking after 300 prisoners face to face," he told media on Thursday.
He said the PSA has voted unanimously to not increase the capacity of the existing facilities, until officers get the same workers compensation entitlements as police.
"We are seeing rising incidents of prison officers getting hurt at work every day," he said.
Steve McMahon, prison officers vocational branch chair said prison guards refuse to go over the agreed capacity of the correctional facilities.
"Prison officers accept they work in a dangerous industry but adding inmates to a system not designed for it, raises the risk to an unreasonable level," he told ABC radio on Thursday.
"It's crunch time," he said.
He said a report from NSW Bureau of Crime Statistics and Research (BOCSAR) shows there were about 9800 inmate beds about 12 months ago but the figure has risen to 10,800 inmates.
"It will be three years until the government builds a facility to house the additional inmates that their own reports are talking about."
Mr McMahon said some facilities have had to put extra inmates into cells that were designed for one or two people.
Meanwhile Corrective Services NSW Commissioner Peter Severin has denied reports that prison officers have threatened to refuse entry to new inmates because of concerns about overcrowding.
"As part of an industrial campaign, the union is refusing to negotiate any new capacity increase," he said in a statement on Thursday.
He also said there is no evidence of increased violence against officers or between inmates.