Cute.
In the first place, employers have the right to restrict what their employees publish. That should go without saying. The First Amendment has nothing to do with it.
Secondly, Drudge hasn't posted the whole memo as yet. It makes no sense to judge the memo on the basis of a couple of quotes, possibly taken out of context. He doesn't yet quote anything in the memo which warns employees to "hold off" reporting on the book.
My suggestion: reserve judgment 'til you've seen the facts.
We as news and information consumers also have the right to question the "objectivity" and "sincerity" of news organizations like CNN. This news outlet is NOT as fair and balanced as some would like us to believe. Progressive viewpoints ARE NOT neutral.
Regards....