True, but I'm thinking more in terms of filing a lawsuit, which opens him to discovery. The judge may quash it as irrelevant, but he shouldn't be surprised by it. It's gonna happen.
Disovery is never as broad as people imagine. It is not an 'open book' on someone's life or business. It only applies to information that is directly relevant to the case AND will be used by the prosecution or defense in the case. Disovery basically prevents hiding of evidence that will be used in the trial.
For example, if the pastor is suing the government employer for personal descrimination, and he has no intention of using his sermons as part of his accusations, then the defense (government agency) has no right to ask for that information as it isn't relevant to the case.
If anything, asking for this type of information can be considered intimidation.