Under what conditions are we not to have fellowship with one "who is called a brother" (1 Corinthian

Under what conditions are we not to have fellowship with one "who is called a brother" (1 Corinthians 5:11)?

Paul gave instructions to the Corinthians not to keep company with those put away, even so much as social eating (verses 9, 11). He likewise instructed the Thessalonians to withdraw from those walking disorderly (2 Thessalonians 3:6) and not to keep company with them (verse 14). When therefore the assembly must deal with an individual whose behavior endangers the behavior of others (1 Corinthians 5:6-8; 2 Thessalonians 3:11) or who needs to learn the seriousness of his sin (2 Thessalonians 3:14), social contact must be limited. In all other cases, saints should cultivate social contact with each other (Hebrews 13:1-3).

D. Oliver