Ministers claim prison officers are being offered an 'attractive' pay deal
Public safety will be jeopardised by plans to change working practices in state-run prisons, the Prison Officers Association has warned.
The Ministry of Justice wants to give low-ranking staff more responsibility as part of a £1bn efficiency drive affecting prisons in England and Wales.
The union's executive has urged members to vote against the proposals in a ballot which closes this week.
However, ministers insist safety will not be compromised.
They say prison staff are being offered an "attractive" three-year pay deal, amounting to almost 5%.
Prisons Minister David Hanson said: "NOMS [the National Offender Management Service] is committed to ensuring the safety of the public, staff and prisoners and we are confident that the proposals... will not jeopardise prison security or safety.
"The offer from the Ministry of Justice represented an extremely good deal for prison staff, particularly in the current economic climate, and a good deal for the taxpayer as it delivers long term efficiency changes."
The Prison Officers Association (POA) is concerned that safety would be put at risk because lower-ranking staff, to be known as "operations officers", would be given greater responsibility.
It is also unhappy that officers will have to undergo tests to prove they are fit enough for the job.
General Secretary Brian Caton told the BBC's Today programme that the proposed pay rises were being offered in exchange for "de-skilling and downgrading".
He added that staff were being asked to "work in increasingly difficult, more populated prisons, without adequate trained staff, and to do it for what was not exactly a huge pay rise.
"So they are trying to bribe us into very dangerous conditions," he claimed.
The Prison Governors Association is due to recommend whether or not its members should accept the deal and leaders have expressed reservations about the plans.
Its president, Paul Tidball, had previously warned of a "serious risk" of disturbances in jails because of a shortage of resources.
He said efficiency measures would not be agreed unless they passed "safety and decency" thresholds.
Juliet Lyon of the Prison Reform Trust said she wanted the POA to show a bit more flexibility.
She said: "What we'd ask is that what's on the table is considered seriously, that there's a proper discussion around a table, and that this isn't the time for taking a stand or a High Noon stance.
"It's important to look at the proposals that are on the table: is that going to be the outcome, or is there going to be an opportunity here to modernise the service."
BBC correspondent Danny Shaw said: "The dispute is likely to become increasingly bitter in the next few days if, as expected, unions reject the plans."