The Congregation for the Doctrine of the Faith is not normally tasked with adding provisions to canon law, but under the direction of the pope, it can do whatever he wants it to.
And it has.
A new CDF document provides a latae sententiae (automatic) excommunication for those who attempt to ordain women and for those women who receive such attempted ordinations.
Congregation for the Doctrine of the Faith
On the delict of attempted sacred ordination of a woman
The Congregation for the Doctrine of the Faith, in virtue of the special faculty granted to it by the Supreme Authority of the Church (cf. Can. 30, Code of Canon Law), in order to safeguard the nature and validity of the sacrament of Holy Orders, decreed, in the Ordinary Session of December 19, 2007:
In accordance with what is disposed by Can. 1378 of the Code of Canon Law, he who shall have attempted to confer holy orders on a woman, as well as the woman who may have attempted to receive Holy Orders, incurs in a latae sententiae excommunication, reserved to the Apostolic See.
If he who shall have attempted to confer Holy Orders on a woman or if the woman who shall have attempted to received Holy Orders is a faithful bound to the Code of Canons of the Oriental Churches, he is to be punished with the major excommunication, whose remission remains reserved to the Apostolic See, in accordance with can. 1443 of the same Code (cf. can. 1423, Code of Canons of the Oriental Churches).
The present decree enters in force immediately after its publication in L'Osservatore Romano.
William Cardinal Levada
Angelo Amato, s.d.b.
Titular Archbishop of Sila
Finally, a few thoughts of my own:
It's interesting, as Ed points out, that the Holy See has gone in the direction of creating a new latae sententiae penalty rather than continuing the trend of abolishing them.
On the part of bishops there may be something of a preference for latae sententiae penalties in that they do not require the bishop to himself take the action of imposing a canonical penalty on one of his subjects--an action that is bound to be portrayed in terms of the harsh disciplinarian stereotype in the popular press. It is much easier for a bishop to say "So-and-so has excommunicated himself/herself by these actions" than "I hereby excommunicate so-and-so for these actions."
I think that in this case, though, there may be an additional and perhaps more fundamental reason for the penalty (at least in the Latin rite) being a latae sententiae one: These ordinations frequently occur in secret.
That's how they got started, after all: If the claims of the original group of female ordinands are to be believed, they found a Catholic bishop somewhere who was willing to perform the initial ordinations. That man's identity has not been revealed.
And subsequent to that event, some of these women have simulated ordination in secret or at least without their identities initially being known to their bishops.
The use of a latae sententiae penalty in this case sends a signal that simply keeping the identities of the parties a secret will not keep them from suffering excommunication. You can't tell yourself, if you are a bishop or a prospective ordinand, "I'm free of canonical penalties as long as nobody knows I did this so that no penalties can be imposed on me."
Instead, the latae sententiae penalty in this case says, "The Church takes this crime so seriously that it provides for excommunication even when the parties, or even the fact, of the crime are unknown."
The same can be said of all the other latae sententiae penalties, such as the excommunication provided for abortion.
One might still question whether we should have latae sententiae penalties in the Latin rite, but I think that the reason for this one is more than just a desire to get bishops "off the hook" for having to impose a penalty. It's a sign of the Church's particularly strong desire to alert those who attempt these ordinations to the gravity of their actions.
Since the current decree is not retroactive, it will not touch those who have previously attempted these ordinations (including the original bishop, assuming that there was one), but it does send the signal going forward to all who would participate in them.