Orange? You're fired!

Sometimes employers do really silly things. Take this law firm that fired 17 employees for wearing orange. Now it did happen the Friday before St. Patrick's day, but there does not appear to be a sensitive Irish logic in the mix. It seems the employer thought the orange shirts were a protest. And as we all know at-will employees can be fired for any reason, even a silly one. The article even quotes an employment lawyer who says just that. But, isn't this protected concerted activity under the NLRA? Surely the employer thought it was, but more than that, if employees choose to dress alike, don't they have a protected right to do that? I think they do.