"Are there any special rules"

Yes. Paragraph #1, sentence #1 of the US Constitution: "provide for the common defence[sic]". This is further elaborated upon in other original Constitution articles and subsequent amendments.

From that, we derive a long, storied history of things, among the more recent of which, and the operative matter here, is the Defense Production Act circa 1950.

The US is fundamentally based on the obligation of mutual military defense, and delegates the authority to call military balls and strikes, such as who will and will not be permitted to contract with the US military, exclusively to POTUS. Anthropic et al. are way out of their depth when they imagine their "terms and conditions" imbue them with some sort of military veto power in the US. Trump's action here, given his nature, is actually moderate: he could take this much further if he wishes.