Vermont Gov. Peter Shumlin signed the nation's first unconditional mandatory GMO labeling legislation into law Thursday in what foes of bioengineering are calling a major victory.

"Today I was proud to sign the nation's first law requiring GMO labeling," Shumlin, a Democrat, said in a statement posted on his Facebook page Thursday afternoon. "Vermonters and Americans have the right to know what is in their food. It's common sense. There is no doubt those opposed to this measure will put up a fight."

The new law is the first in the nation to require a state to begin labeling foods that contain genetically modified ingredients no matter how other states' lawmakers decide to address the issue. Connecticut and Maine had already passed GMO labeling laws, but the launch of their labeling regimes does not begin unless other states pass similar bills.

GMO critics say that there has not been enough testing done on genetically modified seeds and crops, and point to studies suggesting that they could harm the environment and human health. They also argue that consumers have a right to know what they are eating, pointing to individual countries and localities, including New Zealand, Tasmania in Australia and California's Mendocino, Trinity and Marin counties, that have banned the planting and cultivation of GMO crops.

Under the new law, the Green Mountain State will begin requiring food manufacturers to label GMO foods in July 2016 unless other factors preclude it from doing so. One major threat is potential lawsuits brought by Big Ag firms and food producers, who have threatened to sue and argue that GMOs are safe and that labeling should be regulated at the federal level rather than in a piecemeal, state-by-state manner. Congress is considering federal legislation that could supersede such state laws.

"State labeling laws such as the one signed into law today demonstrate that the GMO labeling discussion deserves a national solution," Cathleen Enright, executive vice president for food and agriculture for the Biotechnology Industry Organization trade group said in a Thursday statement. "Such an approach has been proposed in the U.S. Congress in the form of the Safe and Accurate Food Labeling Act (H.R. 4432), which appropriately confirms and explicitly places the authority to require food labeling in this area with the U.S. Food and Drug Administration.”

The Vermont bill's passage is seen as a major rebuke to companies like Monsanto Company (NYSE:MON), DuPont Co. (NYSE:DD) and Syngenta AG (NYSE:SYT), which are engaged in an international public-relations battle to defend the controversial bioengineering technologies behind their GMO seeds. The legislation will also make it illegal for foods containing genetically modified ingredients to be labeled "natural" or "all natural."