A federal appeals court refused to block an order barring Tyson Foods Inc. from advertising that its poultry products don’t contain antibiotics thought to lead to drug resistance in humans.

The 4th Circuit Court of Appeals in Richmond, Va., denied on Wednesday a motion by Tyson to stay the order pending appeal. The Springdale, Ark., food giant had asked the court to stay a ruling by a Baltimore judge, who issued a preliminary injunction last week barring the advertisements while the case is pending.

Tyson issued a statement Thursday saying it is not currently running any advertisements and is working with stores to remove marketing materials by a May 15 deadline set by U.S. District Judge Richard Bennett in Baltimore. Tyson added that it is weighing its legal options and continues to believe it has acted responsibly.

The lower court ruling was a victory for rivals Perdue Farms Inc. and Sanderson Farms Inc., who are suing to stop the advertisements, which they claim are misleading because none of the companies uses those types of drugs and shoppers could be led to think other companies use the drugs.

Bennett said in his ruling that he was “satisfied that the consumer public is being misled” by the “Raised Without Antibiotics” advertising. The ruling affects all advertising and marketing, but not package labeling, which is regulated by the United States Department of Agriculture.

Charles Hansen of the Truthful Labeling Coalition, whose members are Perdue, Sanderson and Livingston, Calif.,-based Foster Farms, said his group had asked the USDA to rescind approval for labeling with the statement “Raised without antibiotics that impact antibiotic resistance in humans.”

Tyson, Perdue and Sanderson say they all use feed containing ionophores, which are largely considered to be antibiotics. However, the substances are not used in humans and thus are not believed to raise human health concerns.

Last spring, the USDA said Tyson could label its foods as “raised without antibiotics,” but the federal agency later reversed that decision after Tyson had spent money on advertising and packaging. Tyson was eventually allowed to use the claim “raised without antibiotics that impact antibiotic resistance in humans.”

Sanderson, based in Laurel, Miss., has argued it lost a $4 million account to Tyson because of the advertising campaign, and Salisbury-based Perdue claims it has lost about $10 million in revenue since last year.

Bennett ruled that the qualifying language was not understood by a substantial portion of the consumer public and that the advertising “may even reinforce consumer misconception.”