The Pennsylvania Department of Agriculture is putting the kibosh on the increasingly popular milk labels that say dairy cows were not treated with artificial growth hormones.

The move surprised Wawa Inc., which just last week joined the rush of retailers and milk processors that say their milk will not be produced with the aid of artificial growth hormones, which are used to boost production.

"Early on, we've had some positive feedback," Wawa spokeswoman Lori Bruce said today. "We think that consumers want to know."

Wawa's label says that the farmers it buys raw milk from have pledged not to use rBST, or recombinant bovine somatotropin. The label includes notice that the U.S. Food and Drug Administration has found no significant difference between milk from treated and untreated cows.

The state change in labeling guidelines, which blindsided many in the industry, is part of a broader effort by the Pennsylvania agriculture department to crack down on labels that highlight what is not in a product, such as "antibiotic-free" and "pesticide-free."

The department said today that it had examined labels from 140 companies and notified 16 companies that they would have to correct their labels by Jan. 1. Those labels contain variations on the claim that cows were not injected with synthetic growth hormones. Three also include a "no antibiotics" claim.

Agriculture Secretary Dennis Wolff said in a news release that "antibiotic-free" and "pesticide-free" are misleading because all processed milk sold in the state is tested a minimum of 10 times for such substances, which are not permitted in milk.

The problem with the claim that cows are not treated with synthetic hormones is that there is no way to distinguish between the natural growth hormone in milk and the artificial version, Wolff said.

Advocates for sustainable agriculture favor the label regarding artificial growth hormones, especially if a more stringent verification process can be established.

"The consumer needs to be able to make a choice and needs to have the information to make a decision," said Leslie Zuck, executive director of Pennsylvania Certified Organic, a nonprofit in Centre Hall, Pa., that certifies organic farmers.

Contact staff writer Harold Brubaker at 215-854-4651 or hbrubaker@phillynews.com.