Without any comment, the justices let stand a ruling by a U.S. appeals court that upheld the constitutionality of the federal law, the Freedom of Access to Clinic Entrances Act.
The law, adopted by Congress in 1994, prohibited the blocking of access to clinics, and the injuring or intimidation of abortion-seeking women or clinic staff.
The U.S. Justice Department (news - web sites) initially brought a civil lawsuit under the law against more than 25 individuals who took part in three blockades in 1996 and 1997 at a reproductive health clinic in Englewood, New Jersey.
A federal judge issued a preliminary injunction barring the defendants from blocking the clinic's doors. The judge also ruled the law was a valid exercise of Congress's authority under the Constitution's Commerce Clause.
A U.S. appeals court upheld the law's constitutionality, a decision consistent with every other federal appeals court ruling on the issue.
In appealing to the Supreme Court, attorneys for the individuals argued the law was not a valid exercise of federal authority because the conduct could be regulated by local law enforcement authorities.
But the Justice Department strongly disagreed, saying Congress adopted the law in response to a violent, nationwide campaign to inhibit women's access to abortion services and to overwhelm local law enforcement.
Justice Department lawyers said Congress found existing laws were inadequate to deal with the problem. They said Congress had the power to prohibit violent and obstructive conduct that substantially affected interstate commerce.