The South Australian Public Service Association says there has been a "catastrophic breakdown" at the Adelaide Remand Centre, which is run by multinational prison operator Serco.
PSA general secretary Charlotte Watson said that on January 27, a remand centre inmate transferring to Yatala Labour Prison was found in possession of 10 grams of cocaine when he arrived.
"This is not a small amount of cocaine, this kind of weight would make Diego Maradona blush," she said.
"In January, I wrote to the Chief Executive of Correctional Services, David Brown, and told him having 10 grams of cocaine in circulation was totally unacceptable.
"This cocaine bungle is the tip of the iceberg, assaults on corrections officers and chronic understaffing has made Serco's continuing management of the Adelaide Remand Centre untenable."
Last week, three correctional officers were assaulted in two incidents, and last December, 10 officers were assaulted, she said.
"This situation is totally unacceptable, correctional officers have the right to go to work and come home again uninjured … (they) are not punching bags," she said.
The remand centre and Mt Gambier Prison, operated by G4S Custodial Services, are the only privately run corrections facilities in SA.
The union is calling on major political parties to commit to returning the remand centre to public hands ahead of the March 21 state election, and the end of Serco's current four-year contract in June.
Liberal correctional services spokesperson Jack Batty said Labor was "presiding over a prison system plagued by drugs and violence".
"It's not good enough - and a Liberal government will ensure all of our corrections facilities are safe for inmates and staff alike," he said.
Ms Watson said Premier Peter Malinauskas had admitted in 2020 that privatisation of the remand centre wasn't working.
"The question is, will he stand hand on heart ... on the eve of an election in 2026 and commit to returning it to public hands?," she said.
Corrections Minister Rhiannon Pearce said the government remained committed to ensuring all prisons operate with the safety and security of prisoners and staff as the utmost priority.
"If re-elected, the Malinauskas government will continue to monitor the performance of government contractors and whether they continue to provide the best value for money," she said.
"I am advised by the department that staffing levels at the Adelaide Remand Centre are currently at an appropriate level."
But Ms Watson said the remand centre needed around 33 staff on day shift, and "some days there are as few as 15 to 20 staff on deck".
In January a prisoner had his jaw broken, the population swelled to 308 inmates when the contracted capacity is 274, and critically low staffing was reported across shifts, she said.
