There is a legal doctrine under which courts will refuse to enforce clauses that are against public policy. Some examples include: racially restrictive deed covenants, inheritance bequests contingent on remaining unmarried, and contracts where one party agrees to perform an illegal act.

In this specific case, the non-disparagement clause would probably be construed not to cover things like testifying before a legislative body or communicating with regulators, even if those communications were voluntary rather than subpoenaed.