It is held that correspondence between a citizen and Parliament cannot be suppressed by anyone for any reason. If a CASA person threatened retribution against someone for communicating with a parliamentary member, it. is up to the privilege committee to investigate and decide if it is interference. If it is they can call it contempt and in theory, get locked up until you purge the contempt.
Courts have much the same rules. I was once asked by a Board to inflict a ‘Clutz” (clayton Utz) employment contract on our staff. The idiots included a clause saying employees agreed not to approach a court to enforce the contract. It was pointed out that any and all judges would go apoplectic if they ever saw such a contract because you can’t prevent someone accessing Government.