When is it a duty to correct prelates?

Christian Brugger's piece in the National Catholic Register today brought to mind St. Thomas's statement that "ubi immineret periculum fidei, etiam publice essent praelati a subditis arguendi."  (ST. II-II, q. 3, art. 4, ad 2).  

Has anyone seen reputable discussions of what qualifies as "ubi immineret periculum fidei"?  Or who is obliged to correct?  I can't imagine that everyone would be obliged to correct their bishop and the Pope, even if they were required to privately reject the expressed behavior or position.  Nevertheless, it might apply widely, since, as Thomas says in the response, "correctio fraterna, quae est actus caritatis, pertinet ad unumquemque respectu cuiuslibet personae ad quam caritatem debet habere, si in eo aliquid corrigibile inveniatur."

I am sure that Brugger's behavior is correct.  I am wondering whether it is obligatory on some, and whether it counts as fraternal correction or not.  

Brugger's piece is here: http://www.ncregister.com/daily-news/pope-francis-and-contraception-a-troubling-scenario/