Justice and Correctional Services Minister Ronald Lamola on Monday told members of Parliament the release of 19,000 prisoners was necessary.
MPs questioned Lamola about the move, which will see thousands of low-risk offenders paroled to curb the spread of COVID-19 behind bars.
The virus has already claimed four lives at correctional centers.
Lamola gave Parliament’s justice and correctional services committee a political overview of his department’s plan.
He said it was informed by the number of positive tests picked up in some Eastern Cape and Western Cape prisons.
“The current COVID-19 pandemic has highlighted the requirements to reduce the number of people in correctional centers.”
Lamola said although the virus has infected less than 1% of the prison population, overcrowding was a threat that would undermine efforts to fight the virus.