If the CEO makes it harder to land contracts or recruit talent, that's a direct impact to working conditions. I loved SpaceX and would consider working there if not for Musk, for instance.

No, that's a very indirect impact to any one individual's working conditions.

FWIW, I think firing the organizers is an overreaction and that it would be in SpaceX's best interest to muzzle Elon, but it's hard to conjure up a legal argument that they can't do it. And you'll notice that the company's statement said nothing about the content of the letter, only that it's inappropriate to organize it with company resources and on company time.

Of course the company says organizing shouldn't happen on company time/resources. Can't be having the workers thinking they could collectively act!

Considering how simple-minded and toxic work-cancer employees are, and how harmful and corrupt a union can be; it is no surprise that Musk is 3 steps ahead of them.

What wouldn’t count as working conditions under such a broad standard? Could I circulate an open letter demanding that I get a tech lead position instead of my rival because I don’t think people will enjoy working on their team? Could a salesperson circulate an open letter demanding that you should be punished because your bad engineering cost the company a big contract?

Unconvincing examples, because those are simply personal grievances and unrelated to broader company culture.

What I'm saying is that I think the open letter's attack on Musk was also a simple personal grievance. The signatories don't like Musk, they're distracted and embarrassed by his Tweets, so they demand that the company denounce him. (The letter said more than that, but if broader systemic reforms were their primary goal, why include an inflammatory attack on one specific executive?)

The courts have covered this. Generally, individual grievances are not protected. Whistleblowing may not be protected. Egregious or offensive language or coerced speech is not protected. Language that is disparaging without being an attempt to improve conditions is not protected.

Wouldn’t a counter point be that the CEO’s behavior filtering out employees that care about Tweets deeply be positive?

Knowing that people like you with your reasons for not working there are not present and harassing people towards your view point could be a recruitment draw no?