Port Augusta Correctional Officers walked off the job along with officers right across the state on Monday to protest the privatisation plans of the Adelaide Remand centre.
Prisoners were put into lockdown as 97% of the workforce walked out and protested in Gladstone Square.
Minimum levels of staffing were maintained during the lockdown, leaving just 18 staff members on site.
Those who attended the rally said that the protest was about the bigger issue of privatisation across the public sector.
Local MP Eddie Hughes was in attendance and told the Transcontinental that prison systems need to be retained in public hands as a matter of public interest.