What is the baptism requirement for becoming a Mennonite?

Historically, Mennonites and other Anabaptists practiced adult re-baptism when a Catholic or Lutheran converted. This got them in a lot of hot water at the time. As a long-time member of a General Conference Mennonite Church (now the [Mennonite Church USA](http://www.mennoniteusa.org/)) , and a current member of a [Mennonite Brethren](http://www.usmb.org/) church, my impression is that when a Catholic (or other person baptized as an infant) becomes a Mennonite, they are generally given the option of re-baptism, but it's not considered a requirement. But admittedly, this doesn't happen very often in the U.S. And in Mexico, where practically everyone is born Catholic (and therefore baptized as an infant), re-baptism seems quite common; but in Mexico the Catholic and protestant churches are often quite at odds with each other (Mexican Catholics think "Christian" is a dirty word). So my question is: What are the *official rules* among Mennonite churches regarding re-baptism of new members of the Mennonite church?