From the Summa Theologica, IIa-IIae, q.33, a.4. I think this passage gives some good balanced advice for Catholics today. On the one hand, there are those who cannot tolerate that traditional Catholics even dare to criticize the members of the current Magisterium; on the other hand are the traditionalists who do so with a regrettable lack of reverence and charity (I won't rule out that I may be guilty of this myself...). St. Thomas demonstrates here that prelates ought indeed to be corrected even by those under them; and publicly only when there is a danger to the faith; and always with charity.
Whether a man is bound to correct his prelate?
Objection 1. It would seem that no man is bound to correct his prelate. For it is written (Exodus 19:12): "The beast that shall touch the mount shall be stoned," [Vulgate: 'Everyone that shall touch the mount, dying he shall die.'] and (2 Samuel 6:7) it is related that the Lord struck Oza for touching the ark. Now the mount and the ark signify our prelates. Therefore prelates should not be corrected by their subjects.
Objection 2. Further, a gloss on Galatians 2:11, "I withstood him to the face," adds: "as an equal." Therefore, since a subject is not equal to his prelate, he ought not to correct him.
Objection 3. Further, Gregory says (Moral. xxiii, 8) that "one ought not to presume to reprove the conduct of holy men, unless one thinks better of oneself." But one ought not to think better of oneself than of one's prelate. Therefore one ought not to correct one's prelate.
On the contrary, Augustine says in his Rule: "Show mercy not only to yourselves, but also to him who, being in the higher position among you, is therefore in greater danger." But fraternal correction is a work of mercy. Therefore even prelates ought to be corrected.
I answer that, A subject is not competent to administer to his prelate the correction which is an act of justice through the coercive nature of punishment: but the fraternal correction which is an act of charity is within the competency of everyone in respect of any person towards whom he is bound by charity, provided there be something in that person which requires correction.
Now an act which proceeds from a habit or power extends to whatever is contained under the object of that power or habit: thus vision extends to all things comprised in the object of sight. Since, however, a virtuous act needs to be moderated by due circumstances, it follows that when a subject corrects his prelate, he ought to do so in a becoming manner, not with impudence and harshness, but with gentleness and respect. Hence the Apostle says (1 Timothy 5:1): "An ancient man rebuke not, but entreat him as a father." Wherefore Dionysius finds fault with the monk Demophilus (Ep. viii), for rebuking a priest with insolence, by striking and turning him out of the church.
Reply to Objection 1. It would seem that a subject touches his prelate inordinately when he upbraids him with insolence, as also when he speaks ill of him: and this is signified by God's condemnation of those who touched the mount and the ark.
Reply to Objection 2. To withstand anyone in public exceeds the mode of fraternal correction, and so Paul would not have withstood Peter then, unless he were in some way his equal as regards the defense of the faith. But one who is not an equal can reprove privately and respectfully. Hence the Apostle in writing to the Colossians (4:17) tells them to admonish their prelate: "Say to Archippus: Fulfil thy ministry [Vulgate: 'Take heed to the ministry which thou hast received in the Lord, that thou fulfil it.' Cf. 2 Timothy 4:5." It must be observed, however, that if the faith were endangered, a subject ought to rebuke his prelate even publicly. Hence Paul, who was Peter's subject, rebuked him in public, on account of the imminent danger of scandal concerning faith, and, as the gloss of Augustine says on Galatians 2:11, "Peter gave an example to superiors, that if at any time they should happen to stray from the straight path, they should not disdain to be reproved by their subjects."
Reply to Objection 3. To presume oneself to be simply better than one's prelate, would seem to savor of presumptuous pride; but there is no presumption in thinking oneself better in some respect, because, in this life, no man is without some fault. We must also remember that when a man reproves his prelate charitably, it does not follow that he thinks himself any better, but merely that he offers his help to one who, "being in the higher position among you, is therefore in greater danger," as Augustine observes in his Rule quoted above.