AUGUSTA — More than 150 students, farmers and advocates gathered Thursday at the State House to demand that legislators pass a bill that would immediately require the labeling of genetically modified foods in Maine.

But critics of the proposal also came to the public hearing to warn that the bill might lead food manufacturers to stop selling products in the state.

The measure would effectively speed up implementation of a labeling requirement passed in 2014 and signed by Gov. Paul LePage. The 2014 law says labeling genetically modified foods would be required only after five contiguous New England states, including Maine, agreed to do the same. Vermont and Connecticut have passed similar laws, but neither New Hampshire nor Massachusetts has acted.

Advocates say immediate labeling will increase transparency for consumers who are wary of eating products made with genetically modified organisms, or GMOs, that they say could harm their health or the environment. In particular, they cited a study linking glyphosate, the active ingredient in pesticides commonly used on genetically modified crops, to some forms of cancer.

But critics, including state lobbyists for restaurants, dairy producers, grocers and food producers, argued that the bill would cause food companies to stop shipping their products to Maine because of the cost of labeling them differently for one small state market.

“If food manufacturers and distributors are forced to label their products only for Maine, it’s very likely they will simply bypass our state,” Shelley Doak, of the Maine Grocers and Food Producers Association, said in a prepared statement. “About 90 percent of our food in Maine is imported. Our choices at the grocery store will be greatly reduced.”

GOING IT ALONE, SAFETY OF GMOS

Some opponents also worry about the cost of facing a lawsuit.

So far, only Vermont has passed a law to move forward with labels for genetically modified food without waiting for its neighboring states. But that effort has been stalled after the state was sued by the Grocery Manufacturers of America. Vermont was successful in an important preliminary hearing Monday, but the law has already cost $1.5 million to defend.

“I oppose this bill not because I’m against GMO labeling, but because it’s wrong to put Maine on an island,” said Rep. Jeffrey Timberlake, R-Turner, whose family owns Ricker Hill Orchards, one of the largest apple-growers in the state.

“Maine will be an outlier and our small businesses will be placed in a difficult position.”

Although LePage signed the 2014 law, his administration spoke up Thursday against the proposal that Maine act now.

Ellis Additon, director of the Bureau of Agriculture, Food and Rural Resources at the Maine Department of Agriculture, Conservation and Forestry, submitted testimony in opposition to the bill. Maine’s agriculture department would administer the labeling program if it goes into effect.

The trigger clause “is important to make sure Maine doesn’t go it alone,” Additon wrote. “Without the triggers, we can easily envision Maine being cut off from major supplies of food and related products.”

Bruce Krupke, executive vice president for the Northeast Dairy Food Association, emphasized that GMO products are safe, and are needed to keep food prices low.

“We have all been consuming (GMOs) for more than 20 years,” Krupke said. “The science is sound. The food is safe, and there’s no evidence to the contrary.”

HEALTH IMPACT, THREAT OF LAWSUIT

But supporters of the bill, many of whom gathered for a short rally before the public hearing, said Mainers have an appetite for transparency, and that scientists are still learning about the risks of consuming products that have been genetically engineered, in some cases to work alongside pesticides. The practice of genetic engineering also could do long-term environmental damage, critics say.

Dr. Michael Hansen, a senior scientist at Consumers Union and a researcher on the health risks of GMO products, pleaded for lawmakers to enact labeling in light of recent research connecting a common pesticide used on genetically modified crops with some forms of cancer.

A recent World Health Organization finding signed by 17 of the world’s top cancer doctors found that the broad group of pesticides containing glyphosate, the active ingredient in the popular weed-killer RoundUp, to be a likely carcinogen linked to non-Hodgkins lymphoma.

Many GMO crops are designed to withstand applications of glyphosate, residue of which makes its way onto produce and other products, Hansen said. In 2012, about 280 million pounds of the chemical was spread on crops throughout the United States, he said.

“Labeling of genetically engineered food would allow consumers concerned about residues to minimize their glyphosate exposure,” Hansen said.

Framing the bill as a matter of honesty in advertising and as an essential part of consumer choice, Jonathan Emord, a constitutional lawyer who helped author Vermont’s labeling law, said governments ought not suppress accurate information.

“If you believe in a free market, accurate information is essential to free exercise of consumer choice,” Emord said.

Complicating the matter is the threat of expensive litigation from agribusiness and grocery lobbying groups. In testimony last year before the Legislature, Attorney General Janet Mills warned against removing the contiguous state provision, saying she was unsure she could advocate for its constitutionality.

But Emord said the threat of a lawsuit should not be used as a compelling reason to do nothing.

“Because of the amount of money the (food) industry has involved in this, no matter what you do or when you do it, they will sue,” he said.