General Mills will begin labeling products nationwide that contain genetically modified ingredients — a “watershed” development, according to one consumer group.

Golden Valley-based General Mills said Friday that since it will be forced by July 1 to begin labeling for GMOs in Vermont — the result of a state law there — it will extend GMO labeling nationwide.

Earlier this week, the U.S. Senate failed to advance a bill that would have outlawed states from passing laws that required GMO labeling on packaged foods. The defeat was a blow to the food industry, which has opposed national and state laws requiring GMO labeling.

“We can’t label our products for only one state without significantly driving up costs for our consumers, and we simply won’t do that,” Jeff Harmening, head of General Mills’ U.S. retail operations, said in a post on a company blog Friday. “The result: Consumers all over the country will soon begin seeing words legislated by the state of Vermont on the labels of many of their favorite General Mills food products.”

Labeling for genetically modified ingredients has been a contentious topic the past few years. The food industry claims that such labels are unnecessary because GMOs were long ago approved by federal food safety regulators. A growing number of consumers have been suspect of GMOs nonetheless, and GMO-labeling proponents say they have a right to know what’s in their food.

“By any measure, today’s development is a watershed moment in the fight for more transparency,” said Scott Faber of the Environmental Working Group. “I applaud General Mills. They’re going to disclose the presence of GMOs and give everyone factual information. This is terrific for consumers.”

Still, General Mills hasn’t altered its support for national legislation that would bar state labeling laws, without requiring national GMO labeling.

“Our position on GMO labeling hasn’t wavered at all,” Harmening said. “We are fully aligned with the Grocery Manufacturers Association,” a big trade group pushing against mandatory labeling in Congress. The association also has filed a federal suit arguing the Vermont law is constitutional.

Campbell Soup Co. is the only major U.S. packaged food company to break ranks with the industry by announcing in January that it supports national, mandatory GMO labeling and are ready to add GMO information to labels by the Vermont deadline.

Several states have had referendums or legislative votes to require GMO labeling, but Vermont is the only one to pass such a law and put it into effect.

“One small state’s law is setting labeling standards for consumers across the country,” the Grocery Manufacturers Association said in a statement, adding that it’s “a serious problem for businesses.”

Alexia Howard, a stock analyst at Sanford Bernstein, said other packaged food makers are likely to follow General Mills.

“The Vermont situation looks now like it is coming to fore so the companies have to do something,” she said. “They basically have a choice: They don’t participate in Vermont or they label the product nationally.”

For a food manufacturer, it makes little economic sense to label products just for Vermont, one of the smallest U.S. states with a population of 627,000, about 20 percent of the Twin Cities metro area.

And if a food company ignores the Vermont law, it could incur significant fines.

“It’s really unmanageable to exclude your product in Vermont or ship (GMO-labeled) product just to Vermont,” Harmening said in an interview with the Star Tribune. Due to production schedules, food makers must start labeling for Vermont soon. “It’s not like you can flip a switch on June 15 and have your (GMO-labeled) products on shelves July 1.”

Vermont requires that labels say an item is either produced with genetic engineering, or partially produced with genetic engineering, depending on the weight of GMO-derived ingredients. General Mills will place the GMO information near the ingredients list on food labels, in about the same-sized type.

Most corn, soybeans and beet sugar produced in the United States are grown from genetically modified seeds. Thus, supermarkets are filled with thousands of products containing ingredients that are qualified as GMO-derived.

General Mills also said Friday it has added a search tool on its website, ask.generalmills.com, to provide GMO ingredient information for hundreds of U.S. products.

So what will General Mills do if the food industry ultimately prevails in Congress with a ban on state labeling laws — or in federal court with a ruling against Vermont? Will the company then drop GMO labels? Harmening declined to speculate.

In the meantime, General Mills can bask in the approval of GMO labeling advocates. “It’s great decision for General Mills to be a leader on this,” said Heather Flesland, director of the labeling group Right to Know Minnesota.