In the ever more litigious society we live in, I'm sure some jackass attorney could find a case. The point wouldn't be so much to win, but to push Walmart in to acting correctly and firing these people and sending a message to every other employee that such blatant discrimination will not be allowed under their name...
You can sue for anything or everything. But if there is no grounds, it is a losing effort, and will get chucked. I can sue the U.S. government for $100B because a bird sh1t on my windshield. Likely, nothing will come of it, and the bird will not be inclined to sh1t elsewhere.
Just so many stories like that. I pray to whichever god anyone chooses that police stop policing certain areas where they are obviously not welcome. If these areas have people getting robbed maimed or even killed, like the first person to reply to this thread, I shall simply say... "Who cares"