The Public Service Association (PSA) says it will not allow any more prisoner transfers until the Correctional Services Department acknowledges overcrowding in South Australia's prisons system.
Representatives from each of the state's jails have had talks in Adelaide, just days after unrest at Port Augusta prison.
Jan McMahon from the PSA says overcrowding is at crisis levels and prisoner transfers will not be supported until the issue has been addressed by authorities.
But SA Correctional Services Minister Carmel Zollo says the PSA must be willing to co-operate with the Government and prisoners need to be transferred.
For its part, the SA Opposition wants an independent inquiry into last week's Port Augusta prison unrest.
Liberal correctional services spokesman Stephen Wade says the Government has been denying prisons are overcrowded even though a Productivity Commission report put them at 22 per cent above capacity.
Mr Wade says the Government insists the trouble was not due to any overcrowding.
"We says that if a space was designed for one person then to put more than one person in there is overcrowding," he said.
"That to us is commonsense. The Productivity Commission, the independent arbiter, says that we are the most overcrowded prison system in the nation at 22 per cent."
SA prison stand-off inmates relocated
They have access to the oval only once a fortnight and that's the particular exercise that was cancelled for operational reasons.
Rioting reported at Pt Augusta prison
The latest banner sprawled in big black letters on a large white sheet says "Assault prisoners hey? No more".
Indonesia tells bombers families get ready
8 years ago