The ruling is a setback as well for efforts to find nationwide solutions for similarly vast product-liability litigation over breast implants, cigarettes and other items. The settlement would have precluded all future claims against the 20 companies.
Asbestos is a heat-resistant mineral once used widely in insulation and fireproofing.
It has been found to cause severe and sometimes deadly respiratory problems. Justices Stephen G. Breyer and John Paul Stevens dissented, and Justice Sandra Day O'Connor did not participate in the case. A conference committee issued a final draft of the rule amendments last year, and the conference is expected to vote on the proposal in September. It was not immediately clear what effect Wednesday's decision would have on that vote. Chief Justice William H. Rehnquist presides over the 27-judge Judicial Conference.