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), and a current member of a Mennonite Brethren 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?