Freedom of expression is enshrined in various documents. Consider this:

Everyone has the right to freedom of opinion and expression; this right includes freedom to hold opinions without interference and to seek, receive and impart information and ideas through any media and regardless of frontiers. (Universal Declaration of Human Rights, s. 19)

Or this:

Everyone has the following fundamental freedoms:

(a) freedom of conscience and religion;
(b) freedom of thought, belief, opinion and expression, including freedom of the press and other media of communication;
(c) freedom of peaceful assembly; and
(d) freedom of association.(Canadian Charter of Rights and Freedoms, s. 2)