The ruling by the San Francisco judge affects doctors who work at 900 Planned Parenthood clinics nationwide. The decision combined with a similar one hours earlier in New York will cover a majority of the abortion providers in the United States.
On Wednesday, a federal judge in Nebraska made a similar ruling that covered four doctors, who together are licensed in 13 states across the Midwest and East, and their staffs. That ruling came less than an hour after Bush signed the law.
U.S. District Judge Phyllis Hamilton of San Francisco ruled the law appears unconstitutional because it provides no exemptions for a woman's health. The basis for her ruling mirrors the reasons cited by the other judges.
Hamilton called the new law "an undue burden on a woman's right to choose."
In New York, U.S. District Judge Richard Casey granted a request by the National Abortion Federation and seven doctors to prevent enforcement of the ban until a challenge to the law's constitutionality can be heard.
While the ruling applies only to the plaintiffs, it is expected to have broad application: The federation — a professional association of abortion providers in the United States and Canada — says that its members perform half of abortions nationwide.
The new law outlaws a procedure generally performed in the second or third trimester in which a fetus is partially delivered before being killed, usually by puncturing its skull. Anti-abortion activists call the procedure "partial-birth abortion." President Clinton twice vetoed similar bills.
Abortion-rights advocates expect a showdown over the law with the Bush administration at the U.S. Supreme Court.
The Justice Department said in a statement that it "will continue to strongly defend the law prohibiting partial birth abortions using every resource necessary."
Douglas Johnson, a spokesman for the National Right to Life Committee, said the New York judge's ruling was "not surprising but it is distressing."
"It means that partly born babies will continue to die at the point of 7-inch scissors," he said. "Certainly these judicial orders severely impede the government's ability to protect these premature infants."
Opponents of the law said it is overly broad, lacks any exemption for the health of a woman seeking an abortion and could outlaw several safe and common procedures. They also contended it is the first step in a larger campaign to ban all abortions and undo Roe v. Wave, the Supreme Court's 1973 landmark decision establishing a woman's right to an abortion.
"It's not unusual for a law like this to be challenged," says CBSNews.com Legal Analyst Andrew Cohen, "and certainly the lawmakers who drafted it should have known that some judges would find it unconstitutional."
Cohen adds: "The question is whether federal appeals court judges are going to do the same and whether the U.S. Supreme Court ultimately decides to get involved."
The judge in New York said it is clear that some doctors believe the outlawed procedure is necessary to protect some women's health. He said there is a good chance that those challenging the law will succeed.
"It's hard to imagine the federal government would try to enforce the law against anyone who might be providing abortions but is not a member of the protected group," said Donna Lieberman, executive director of the New York Civil Liberties Union.
American Civil Liberties Union attorney Talcott Camp said it "would be quite troubling indeed if the Justice Department attempted to enforce" the ban while the challenges are pending.
"Many physicians were indeed panicked at the prospect of having to face criminal prosecution for providing the absolute best medical care they can," she said.
In addition, legal observers said the Nebraska ruling might be more sweeping than first thought. They said the ruling is worded in such a way that it could allow abortion doctors across the country to skirt the law.
While the judge stopped short of saying his order was to be enforced nationwide, he said it applied to the four doctors who filed the suit and their "colleagues, employees and entities ... with whom plaintiffs work, teach, supervise or refer" patients.