Workers at the Appin and Dendrobium longwall mines in New South Wales have been removed from areas that they may require use of CABA in an emergency while every unit is thoroughly checked.
The masks are kept on standby in case underground mineworkers need to evacuate, according to the Construction Forestry Mining and Energy.
A South32 spokeswoman told Australia's Mining Monthly that routine testing has discovered an issue with some of the CABA units at the Appin and Dendrobium mines.
"The devices provide breathable air in the event of an underground emergency," she said.
"The safety and wellbeing of our people is paramount and we have voluntarily withdrawn our underground workforce at both mines.
"We are working to ensure a safe and orderly return to production and do not expect any material impact on shipping obligations or production guidance."