In the Gospel Jesus tells us to warn a brother or sister who is going wrong. For the most part, we do well to hold back on pointing out our neighbor's wrong doing, but that is not always the case.
The third of the Gifts of the Holy Spirit is the offering of counsel when it is called for. The Letter to the Hebrew speaks to this need.
'If you are without discipline you are not sons, but bastards. . . At the time, all discipline seems a cause not for joy, but for pain, but later it brings the peaceful fruit of justice to those who are trained in it."