You said they broke the law by asking managers to tell them on a hotline whether or not they had noticed any union activity. There should be a specific spot in the law that says that. Where in the NLRA does it say that?
Nothing in that link shows that. In fact, it contradicted it. If "seeing people doing union activity is not spying", then clearly managers are able to tell their bosses that they saw it. As in, on a hotline.
In fact, the actual law also says that employers can't "Prohibit employees from talking about the union during working time, if you permit them to talk about other non-work-related subjects." That implies that if an employer doesn't permit any talk about non-work subjects, they are well within their rights to prohibit talk about union subjects during work time.
Which also means that the only reason employees are able to discuss unions at work at all, is because employers have permitted them to do so.
I would have thought discussing the union would be considered "a work related subject"