A container was left precariously hanging over a truck at Patrick Port Botany on Monday when the company's automatic Rail Mounted Gantry (RMG) failed.
Sydney Branch Deputy Glen Wood said the accident could have been fatal.
"Comrades, Do we have anything to fear with the industry going Auto? Not at the moment, all we have to fear is our members being killed," he said. "See the photo of what happened yesterday afternoon at Patrick's Port Botany."