It doesn't seem like lawsuits going after employers who post such rules, yet fail to provide security, have had much success. Maybe this should be another project for SAF.
At first, that seems like a good idea, until one realizes that the concept tramples all over private property rights.
Private property, and the control of it, is one of the cornerstones of liberty. We may think we're well-intentioned by requiring property owners to allow firearms, but think through the implications.
If a law passes requiring me to allow people to carry in my store, you can bet there will be a law that requires me to allow people to demonstrate their political views on the premises. I will have to take anybody's check, written on any bank. There will be a law that I can't dictate what people wear or don't wear. There will be another in which I can be sued because my fluorescent lighting causes depression.
Well-intentioned as it may be, it's a dangerous and slippery slope. Furthermore, I can't see that it would ever fly in the courts.
Michigan is an "at will" state, so Walgreen's can fire the guy for any reason, short of discrimination. It stinks, but he knew the rules when he started.