wjstix:I guess you could have an exception like the old Erie Mining Co. in Minnesota, whose railroad crews were members of the miner's union and had to wear hardhats when operating trains
Before my Mother married she worked as a nurse at the hospital in Canmore, AB. This was before government health care came in, and the hospital was owned and staffed by the coal mine at Canmore.
My Father used to kid her about the fact that the only Union Card my Mother ever held was with the United Mine Workers! She didn't have to wear a hardhat, nurses still wore those little white caps.
AgentKid