A further 164 prison officers will be allowed to retire early under a voluntary package within the next year.
The bill for the additional redundancies will be around £30m.
The number of officers taking redundancy will now total more than 500.
By the end of this month, 360 officers will have retired at a cost of £40m.
The Prison Service has written to 164 officers on a waiting list telling them that they can now also take early retirement.
The Prison Service has said the redundancy scheme is essential for a new beginning.