This does not mean, though, that the person is not welcome in the church for the purpose of this discipline is to bring the person into repentance and reconciliation with God and God's people.
Matt. 18:15-18 ?And if your brother sins, go and reprove him in private; if he listens to you, you have won your brother. 16 ?But if he does not listen to you, take one or two more with you, so that by the mouth of two or three witnesses every fact may be confirmed. 17 ?And if he refuses to listen to them, tell it to the church; and if he refuses to listen even to the church, let him be to you as a Gentile and a tax-gatherer. 18 ?Truly I say to you, whatever you shall bind on earth shall be bound in heaven; and whatever you loose on earth shall be loosed in heaven."
So, the proper steps preceding excommunication are going to the person in private, then with two or more witnesses, then a proclamation to the church if he will not repent. The elders of the church should be involved in this process.