WASHINGTON, Sept. 3 — A federal appeals court issued a surprise order today blocking the Federal Communications Commission from imposing new rules that would make it easier for the nation's largest media conglomerates to add new markets and areas of business.
The decision came a day before the new rules, considered among the most significant efforts at deregulation adopted during the Bush administration, were scheduled to take effect. It followed two hours of oral arguments at an emergency hearing this morning by a three-judge panel in Philadelphia and was a sharp setback for the largest media companies and for the commission's chairman, Michael K. Powell.
Mr. Powell, the architect of the new rules, has emphasized that the commission was compelled to rewrite the old regulations because of a string of federal court decisions in cases brought in Washington by the media companies. Those decisions ordered the agency to reconsider some of the rules.
But today the appeals court voted unamimously to prevent media companies from moving forward with plans to take advantage of the new rules. The court also raised tough questions for the commission and its industry supporters about their efforts to reshape the regulatory landscape. The new regulations are already facing a challenge in Congress, where legislators have taken steps to repeal some of them.