[Update (16:33 EDT): The AP has changed its lede to read "The Vatican insisted Friday that it is properly following Christian tradition by excluding females from the priesthood as it issued a new warning that women taking part in ordinations will be excommunicated." (h/t Damian G. of Conservathink).]
According to the Associated Press, the Vatican is "slamming the door on attempts by women to become priests in the Roman Catholic Church." But it's rather hard to slam shut a door that was never open, which is what Catholic Church teaching holds about women serving in the priesthood.
From a May 30 article entitled "Vatican: excommunication for female priests" (paragraph break removed):
VATICAN CITY - The Vatican is slamming the door on attempts by women to become priests in the Roman Catholic Church. It has strongly reiterated in a decree that anyone involved in ordination ceremonies is automatically excommunicated. A top Vatican official said in a statement Friday that the church acted following what it called "so-called ordinations" in various parts of the world.
Yet far from "slamming" shut the possibility of female priests, the Catholic Church holds that God, speaking to His people through the words of Scripture -- not the Pope or the Church -- bars women from clerical office. This, however, by no means diminishes the role of women in the life of the church, as Catholic apologist Jason Evert explains (emphasis mine):
There were other roles that Christ had in mind for women. For example, they played a key role in the spread of the Gospel, being the first to spread the news of the risen Christ. They were also allowed to pray and prophecy in church (1 Cor. 11:1-16), but they were not to assume the function of teaching in the Christian assembly (1Cor. 14:34-38; 1 Tim. 2:1-14), which was restricted to the clergy.
Two thousand years later, no one-including the pope-has the authority to change the designs of the Church that Christ instituted. Specifically, the Church is unable to change the substance of a sacrament. For example, a person cannot be baptized in wine, nor may a substance other than bread be used for the consecration at Mass. If invalid matter is used, then the sacrament does not take place. Likewise, since the priest acts in the person of Christ, the Church has no authority to confer the sacrament on those who are unable to represent the male Jesus Christ.
One other point: the headline choice is similarly misleading. While the Church considers automatically excommunicated those who participate in "ordination" ceremonies, those ceremonies do not in any way confer the office of priest upon the participants. Therefore no female priests would end up being excommunicated since female priesthood is in and of itself a contradiction in terms under Catholic teaching.