Could employers ask me for my password by default? I mean would it be legal reason to fire me if I not give it to them? Coming from Germany, I am not sure, here

Could employers ask me for my password by default? I mean would it be legal reason to fire me if I not give it to them? Coming from Germany, I am not sure, here apparently it is not so easy to fire somebody, but in the US it might be so easy that it doesn't matter. That is, they don't have to give a reason, which means not getting a password could be a reason? Otherwise I wonder if in the future it will be one more thing to watch out for in contracts. Another aspect: if an employer would be willing to fire you over such a thing, your profession is probably not in very high demand and you should consider switching.