"31- No private person may impose the ban on anyone, except the church, ie., the community of those among whom the person to be excommunicated live, together with its guardian, ie., the minister.
32- Only the person who causes public offense may be banned." (The 67 Articles)
You can read the full text at Jim West's blog: http://zwingliusredivivus.wordpress.com/2010/02/17/the-67-articles-of-huldrych-zwingli/
It would be interesting to find some material from Zwingli that goes into greater depth on these two points. Unfortunately those snobs who hold the key to knowledge on Zwingli refuse to translate his works into english for us un-educated folk. Instead we must spend ten arduous years trying to grasp the german language so we can join in with the esoteric scholars.
In the meantime, some preliminary comments are in order. I'm trying to test these articles against Paul's apostolic instructions on the ban to see whether they hold up. I like the perimeters Zwingli wisely places around the act of excommunication, no doubt to maintain order among Christians. Otherwise we would all be excommunicating each other right left and center. At certain points in history this was precisely the flavor of Mennonite practice (at least in the Netherlands: http://www.plettfoundation.org/Preservings/preservings25-1.pdf, pages 29-34).
"I have written you in my letter not to associate with sexually immoral people..." (1 Cor. 5:9). Zwingli grasps the importance of order and unity that is presupposed in this commandment (cf. 14:40). But what if the church has a sexually immoral brother in its ranks and deliberately does nothing about it? Shall the individual share in this sin of ommission, continuing to associate with the aforementioned brother?
Zwingli's first article seems to leave the observing individual in a particularly bad ethical dilemma. The commandment requires separation from the guilty brother (whose sins have been exposed) but cannot be personally exercised because the idle church refuses to formally acknowledge the guilt.