I believe that's called extortion, and in most states it's against the law.
It would be hilarious if the administration arranged a meeting to discuss the demands with the protesters. Get the protesters to admit that the letter was theirs. After that is done, then the university president could announce "that person is the corner is agent so-and-so of the FBI (or state bureau of investigation, as appropriate) who is here to arrest you on the charge of extortion. This isn't your biggest concern right now but you're also expelled. That concludes our meeting."
Of course, this would never happen but it would be great if it did.