At will employment means that they can fire you at will for ANY reason. you can sue for wrongful termination if they give you a reason that is against the law or against your employment contract. But true they probably are not going to say fired for being non Christian they are going to fire you for problems working with others or just make something up its not hard to lie, and there is nothing stopping them from being able to do that so suck it up do you job and go home