The pope spoke to the Italian bishops' conference, which has called on Italians to boycott the June 12-13 referendum.
He did not mention any details of the law but noted that the bishops were "committed to illuminating the choices of Catholics and all citizens" in the upcoming referendum. He emphasized the importance of defending the family and human life.
While it was his first foray into an Italian issue, the pope's support was not unexpected. Cardinal Camillo Ruini, the head of the Italian bishops' conference, is the pope's vicar for Rome.
For years, Italy had no laws on assisted fertility, giving the country something of a free-for-all
The current law forbids sperm and egg donation, limits the number of embryos created with in vitro techniques to three and bans all embryo research.
The referendum would abrogate the law's provisions on embryo research, the three-embryo limit, the ban on egg or sperm donation from outside the couple and the attribution of rights to the unborn.
Opponents of the law complain it restricts scientific research and a woman's reproductive rights. Some also say it harms women, since it bars the freezing of embryos and thus forces women to be implanted with as many as three embryos.
The ANSA news agency reported that 85 percent of the physicians at Italy's largest gynecological hospital in Turin support changing the law and that more than 100 of the doctors issued a public appeal Monday for Italians to vote.
A communist politician, Franco Giordano, went on Radio Radicale and called the pope's remarks an "unwarranted interference in the affairs of the Italian state."
AP Photo/Domenico Stinellis