It is probably worth knowing that you *can* make agreements about what you will say in most places, including places which take freedom of speech seriously.
Let it suffice to say that the economic conditions lead to me losing a job and the agreement associated with this says things about what I and they say about this matter. One of these terms is that the details of the agreement are confidential.
There are also certain forms of speech which are not allowed, for example incitement to murder. Various sorts of conspiracy are also not protected even in the US.