More than 100 workers at three Adelaide hospitals will walk off the job amid concerns over staffing levels and safety measures.

Workers at the Flinders Medical Centre, the Repatriation General Hospital and the Noarlunga Hospital will take the action on Thursday afternoon over issues the United Workers Union says are putting patients at risk.

"Understaffing issues raised by our members highlight the impact of SA's health crisis, and our members are simply not going to take it anymore," public sector co-ordinator Paul Blackmore said.

"Workers are being left emotionally and physically exhausted as they carry the burden of keeping the hospital system running, fronting up every day during COVID-19.

"Hospital cleaners, catering staff, sterilisation technicians and patient services assistants are calling on the government to give them safe, secure jobs but the government is treating them with contempt."

Mr Blackmore said issues raised by workers ahead of the walk-offs included hundreds of shifts for patient services assistants going unfilled, staff regularly asked to work double shifts and a failure to provide personal protective equipment.

The union said there had been repeated instances across hospitals where correct PPE was either not available, or training not provided on how to use it safely.

Mr Blackmore said the issues highlighted by workers were already the subject of continuing work bans across 46 hospitals and aged care facilities.

"The government only needs to look inside the hospitals to see that the understaffing of these essential workers is also impacting on patient flows," Mr Blackmore said.

"If the government was fair dinkum about fixing the SA Health crisis, they would be making sure their essential health workers had secure jobs and safe workplaces to respond to the COVID-19 pandemic."