The new government says its tougher-on-crime approach will see up to 400 more people sent to prison in the coming year.
But the union representing corrections workers says it is already facing chronic staff shortages, and can't keep up with this year's more than 10 percent rise in the prison population.
There are currently just under 9000 inmates.
The Department of Corrections says it is short about 370 staff right now - meaning the country's 18 jails can't use all of the 11,000 beds across the system. But the Corrections Association says the number needed is closer to 500.
Association President Floyd du Plessis says recruitment and retention is really challenging and the situation poses safety issues.