A federal judge in San Francisco struck down the Partial Birth Abortion Ban Act on Tuesday.

In a strongly worded opinion that accused Congress of misrepresenting many scientific facts about the procedure, U.S. District Judge Phyllis Hamilton concluded that the bill — approved by wide margins in Congress last year and signed by President Bush — was unconstitutional. Hamilton adopted most of the arguments put forward by the Planned Parenthood Federation of America in finding that the measure was too vague, that it placed an unfair burden on women seeking certain kinds of abortions and that it did not do enough to protect women’s health.

The ban on the procedure that critics call “partial birth abortion” was already on hold temporarily as three courts heard legal challenges to it, but Hamilton’s decision specifically prohibits the Justice Department from enforcing the law at any of Planned Parenthood’s 900 clinics, which perform about half the nation’s abortions.

Two other challenges to the law are expected to be decided by other federal judges this summer.

Doctors call the procedure “intact dilation and extraction.” It is unclear how many abortions are performed this way each year, but it is a small percentage. Many abortion providers argue that it is necessary because it can be lifesaving for some women and can protect the fertility of others.

In 2000, the U.S. Supreme Court voted 5-4 to overturn a Nebraska law that outlawed the procedure, ruling it unconstitutional because it did not allow the method even if a doctor believed it was the safest way to preserve a woman’s health. The federal law also provided no exemption if a woman’s health was at stake.

Congress sidestepped the Supreme Court’s earlier ruling by issuing “findings of fact,” including the conclusion that partial-birth abortions are never medically necessary. Hamilton disputed that decision, citing U.S. Supreme Court Justice Clarence Thomas’s opinion in a separate case that courts can overrule legislative judgments on what is fact and what is not. She wrote that by referring to the procedure as “infanticide,” Congress was being “grossly misleading and inaccurate.”