The U.S. Department of Agriculture was not immediately available to comment on when it would allow shipments of Canadian cattle to resume. The imports were banned in May 2003 after a cow in Alberta was found to have mad cow disease.
The unanimous decision by a three-judge panel of the 9th U.S. Circuit Court of Appeals overturns a Montana judge who blocked the USDA from reopening the border in March, saying it "subjects the entire U.S. beef industry to potentially catastrophic damages" and "presents a genuine risk of death for U.S. consumers."
The justices said they would issue another ruling soon explaining their rationale.
The decision came a day after the Justice Department urged the appeals court in Seattle to reopen the border to imports. Justice Department attorney Mark Stern said lifting the ban is based on "good science" and would not result in the "infestation in American livestock."
During the hearing, the three judges suggested that U.S. District Judge Richard F. Cebull perhaps should have given deference to the USDA's decision.
Judge A. Wallace Tashima said the law "does invest the secretary of agriculture with a certain amount of discretion."
Judge Connie Callahan agreed, saying the USDA is "entitled to some deference. It's their whole job to keep up with the science to make those decisions."