Right to the inviolability and transmission of correspondence
Article X. Every person has the right to the inviolability and transmission of his
correspondence.
Article X of the Organization of American States Declaration of the Rights and Duties of Man would seem to prohibit NSA interception and review of email content. That treaty is binding on the U.S. via the Constitution's Treaty Clause. However, the OAS procedural provisions require exhaustion of national remedies before petitioning the Commission for review.