Walk until you bleed, or find another job

Can an employer arbitrarily expand the scope of work to such an extent that it causes physical pain and injury to the workers (specifically expand watch routes so much that people are walking so much their feet are swelling, bruising and bleeding), then tell them (as my supervisors have told me when I approached them to tell them of my pain and injuries) that it is my choice whether or not to work there, and if the injuries I'm experiencing are too great for me to handle, I can always quit and find a job somewhere else? I'm no wimp, but a doubling of the distance walked in steel-toed boots while hauling all the tools and equipment we need to do our job has everyone on the watch complaining about their feet. This is for City and County of San Francisco, Airport Commission.