Perhaps I wasn't clear that that would be my intention.I would find that to be an unacceptable intrusion upon my right to play my character as I see fit. If you want that to be a thing that happens, make it into a spell or the like, give me a saving throw, and some sense of what is at stake so I can make an informed decision about what resources I want to spend to avoid a bad result (Inspiration, for example).
I'd basically say "The fiend is causing psychological torture to you. To prevent yourself from saying anything, you must make a DC13 constitution check or you speak involuntarily. You are free to say whatever if you fail, but you must say something. If you succeed, you tell the fiend nothing for the interrogation scene and it will give up. "
I might make it a saving throw, the specifics are pretty loose at the moment but I do also want to give the feeling that a player might persuade me to use a different ability with their own justification "I'll rely on my willpower (charisma) rather than my physical fortitude (constitution) to prevent myself from speaking."