After citing several relevant scriptures, The Watchtower explained why an unrepentant smoker should be disfellowshipped.
وَٱقْتَبَسَتْ آيَاتٍ عَدِيدَةً تُظْهِرُ أَنَّ مَنْ لَا يَتَوَقَّفُ عَنِ ٱلتَّدْخِينِ يَجِبُ أَنْ يُفْصَلَ عَنِ ٱلْجَمَاعَةِ .‏