The difference as I see it, not explicitly related to this case:
Not ok:
"You there, I need you to become (some class)."
Ok:
"We could need more (some class), everyone. I'm filling up the war chest right now."
Where is the line? The line is NOT whether it's a request or an order. The IR page makes it clear that requests and orders are the same when it comes to IRs.
The difference is whether or not someone is told to change his class. Or you are making a factual statement about the needs of the realm. Semantically speaking, the difference is the object of your speech. If you are talking about the realm in a way that does not address or point towards one or a small number of individuals, that's fine because nobody needs to feel pressured.
