The Irish Prison Officers Association is to begin a fresh ballot on the Government's prison overtime proposals this Friday.
The ballot will take place by post, with results expected on August 17.
An IPOA delegate conference has recommended acceptance of a deal that would see prison officers getting a salary increase and a one-off payment in return for working seven hours overtime every week.
The move is designed to reduce the €60m annual prison overtime bill.
IPOA members have already rejected similar proposals, believing they would be forced to work overtime under the deal.
Justice Minister Michael McDowell has threatened to immediately privatise the prison escort service if they vote against the proposals again this time around.