Matthew 18:15-18

If a brother sins against you, go and point out the wrong to him, just between the two of you. If he listens to you, you've won your brother over. But if he doesn't listen, then take one or two more people with you, so that by two or three witnesses the truth can be confirmed. If, however, he refuses to listen to them, then tell the church. If he refuses to listen to the church as well, then treat him as a foreigner and a tax collector. I tell you the truth, whatever you ban on earth will have been banned in heaven, and whatever you allow on earth will have been allowed in heaven.