An emerging controversy over requiring labels for genetically engineered food arrived at the State Capitol on Thursday.

A few dozen proponents wearing green "Label GMOs" stickers listened to Rep. Karen Clark, DFL-Minneapolis, describe "a bill about the basic right of consumers to know what's in their food."

But opponents said that mandatory labeling would be expensive and confusing, and isn't necessary. The stakes are especially high for large foodmakers and distributors such as Minnesota's Cargill, Hormel, General Mills and Land O'Lakes.

"There is no safety, health or regulatory reason for such a label," said Kelsey Johnson, director of state affairs for the Grocery Manufacturers Association.

At issue are genetically modified organisms (GMOs), produced by manipulating genes in the lab to create new varieties of plants, animals and organisms with desired characteristics, such as corn that will kill rootworm pests that eat it.

The bill would require the words "Produced with Genetic Engineering" to be placed on all packages of food with GMO ingredients that are offered for retail sale in Minnesota. Clark said it would apply to bread, cereal and most processed foods, since about 90 percent of the corn and soybeans grown in Minnesota and nationally comes from genetically engineered seeds.

The proposal is only about labeling, Clark said, and has nothing to do with banning the foods or beverages.

The informational hearing was held to "tee up the issue," said Rep. Joe Atkins, DFL-Inver Grove Heights, chairman of the commerce and consumer protection committee. The bill won't get further action this legislative session, he said, but may return next year if there's enough interest.

Those lining up in support of the bill include food co-ops and natural food stores, some restaurants, the Minnesota Farmers Union and consumer groups such as Right to Know Minnesota. Opposed are many of the larger food producers and processing companies represented by the Minnesota Agri-Growth Council, the Minnesota Chamber of Commerce and the Minnesota Grocers Association.

The question of GMO labeling has popped up in several states recently and seems to be emerging nationally.

Connecticut and Maine passed GMO labeling legislation in 2013, but the requirements don't become effective until neighboring states have also passed similar laws. Vermont's legislature passed a GMO labeling bill this month that is not contingent on other states. Another 30 states are considering new laws or ballot initiatives that would require labeling of GMO foods.

However, a federal bill introduced April 10 would pre-empt states from passing their own GMO labeling laws, and require federal authorities to develop a national voluntary GMO labeling standard.

Liz McMann, consumer affairs manager at Mississippi Market, a natural foods cooperative in St. Paul, said shoppers ask her about GMO-free foods.

"Consumers in Minnesota are food-savvy, and we want to know where our food comes from, and how it was produced," she said. "We're willing to pay more for food that was produced without synthetic pesticides, growth hormones and GMOs."

Tracy Singleton, owner of the Birchwood Cafe in south Minneapolis, said restaurant customers increasingly ask whether the food being served contains GMO ingredients.

"I do not own the patent on GMOs, and I do not profit from them," Singleton said. "In fact it costs me time and money to avoid them, so why do I have to be the one to pay the price to assure my customers that my food does not contain something they don't want in the first place?"

Opponents of labeling said that allowing states to pass separate laws would create a patchwork of confusing rules.

Perry Aasness, executive director of the Minnesota Agri-Growth Council, said national and international scientists and agencies have determined that GMO crops are safe and "essentially identical" to non-GMO crops.

"Requiring labeling of [GMO] foods that are indistinguishable from foods produced by traditional methods would mislead consumers by falsely implying differences where none exist," he said.

Jamie Pfuhl, president of the Minnesota Grocers Association, said additional labeling would put grocers at a disadvantage to competitors in neighboring states and online.

"Mandating unique state labeling requirements will have adverse consequences and limit selection and drive up costs," she said. She advocates a national standard for GMO labels modeled after the organic food standard that suppliers could put on their products voluntarily.

But Anne Tenner, an attorney for the nonprofit National Health Freedom Action, said manufacturers change labels all the time without huge costs or disruption. It's the absence of information about GMOs on food packaging that is misleading to consumers, she said, because they want more information about what they're buying and eating.