Now we command you, brothers, in the name of our Lord Jesus Christ, that you withdraw yourselves from every brother who walks in rebellion, and not after the tradition which they received from us.
There may be some question whether or not a formal excommunication is meant here, especially in the light of  2 Thessalonians 3:15, where the offender is still to be treated as a "brother."  Ecclesiastics have been far too bold in turning this verse to their own purposes.  Morris seems to have caught more accurately the spirit of Paul's words in this place, thus: