The ruling by U.S. District Judge Richard Bennett was a victory for rivals Perdue Farms and Sanderson Farms Inc., who are suing to stop the advertisements.

Tyson operates a poultry processing plant in Shelbyville.

Salisbury-based Perdue and Laurel, Mississippi-based Sanderson argued the advertisements are misleading because none of the companies uses those types of drugs and shoppers could be led to think other companies are using the drugs.

Bennett said he was convinced "that the consumer public is being misled" by the "Raised Without Antibiotics" advertising.

All three companies 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 U.S. Department of Agriculture said Tyson, based in Springdale, Ark., could label its foods as "raised without antibiotics," but the USDA later reversed that decision after Tyson had spent money on advertising and packaging. Tyson was eventually allowed to say its products are "raised without antibiotics that impact antibiotic resistance in humans."

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

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

Tyson issued a statement saying the preliminary injunction does not affect the USDA-approved product label used on Tyson's fresh chicken products. However, the decision does affect point-of-sale materials in stores and the company will seek a stay of the order.

Dave Hogberg, senior vice president of Consumer Products for Tyson Foods, said in the statement that "we firmly believe we have acted responsibly in the way we have labeled and marketed our products."

Attorney Randall Miller, lead counsel for Perdue and Sanderson, said his clients felt the modified language was "more insidious" because it connected the dots to antibiotic resistance, an important consumer safety concern.

Miller has said his clients could make similar claims but feel they are deceptive and have refused to do so. Tyson had said the two rivals were trying to use the courts "to circumvent the regulatory judgment of USDA" and asked Bennett to dismiss the case, a request the judge denied last week.

Tyson's shares closed Tuesday down 67 cents, or 3.5 percent, at $18.77. Sanderson Farms also lost $1.23, or 2.9 percent, to $40.70.