NSW patients will get a free ambulance ride on Thursday when more than 22,000 Health Service Union members go on strike and paramedics work but refuse to bill patients.

Health workers including cleaners, security guards and administration staff will partake in a four-hour rolling industrial action to demand safer workplace conditions in light of assaults and abuse they face at work.

Health Services Union NSW Secretary Gerard Hayes said his members were "taking every precaution possible to prevent any impact on public health".

"Paramedics will continue their revenue strike on the NSW government, declining to collect billing details for patients. Emergency services will not be affected," he said.