Hold your tongue
First of all, ew. (Ever tried it? Strange sensation.) Second of all, not what you wanna hear as a voice actor. But there are times when you're asked to do so, to spare another or to fulfill an obligation; and for someone who enjoys talking, that's a difficult thing.
So how do you choose when to and when not to?
Before I started this blog, I spoke to someone who had more experience with this sort of thing than I did, and asked his advice (in particular, regarding posts about events that, while the events affected me, they did not directly involve me). He told me about a friend of his who blogs and speaks regularly on a delicate issue. His advice boiled down to 'who does it hurt?'
Does what you choose to say, through the spoken or written word, benefit or harm someone?
There is the situation in which you're asked to keep silent in order to protect the work you do. If you're in a situation that involves a contract and a non-disclosure agreement (if you're in that situation, well done, you), keeping silent protects your paycheck and protects the audience from spoilers. Fair enough.
But when it comes to a wrong that's been done, it's another matter. You don't want to rock the boat. Fine. But there are still practices that damage, not only yourself, but others in your situation. There are problems that need to be solved that you can't solve on your own. Silence here doesn't benefit anyone, and the choice between keeping the peace and fixing the problem becomes a choice between rocking the boat or watching it sink.
And I'm not a fish.
ETA: That friend of the guy I spoke to? She's doing a lot more good speaking up about her issue than she would if she didn't. If you're curious about it, let me know. I'll ask her permission to get you guys in contact.