Many of us know intuitively that genetically modified foods are unsafe to eat and that they are harmful to the environment and other living beings, but there could be a much bigger concern: they may actually threaten the stability of the world’s food supply.

Most Americans don’t realize that they probably eat GM foods every day, but it’s generally agreed that about 80 percent of the US food supply contains some form of GMOs. The US Department of Agriculture estimates that 90 percent of US soybeans, sugar beets and corn is genetically modified, and food ingredients made from those crops – like high fructose corn syrup, dextrose, soy lecithin and corn starch – are found in most processed and packaged foods, sodas, and cereals.  Corn is also a staple animal feed, so most US-grown meat is raised on a diet of GM grain as well.

According to the International Service for the Acquisition of Agri-biotech Applications (ISAAA), an international nonprofit that promotes biotechnology, the US is the largest global producer of GM crops, accounting for 40 percent of the GM acres planted worldwide. Much of that land is planted with crops developed by biotech giant Monsanto, which owns 1,676 patents for seeds, plants, herbicides and other agricultural products.

The numbers from ISAAA left me with my jaw hanging open:

Monsanto controls 80 percent of GM corn and 93 percent of GM soy in the US; that translates to 72 percent and 84 percent of the nation’s total output of corn and soy, respectively. Forty percent of total US cropland (over 151 million acres) was planted with Monsanto seed in 2013. Worldwide, 433 million acres of GM crops were grown in 2013 by 18 million farmers, and a staggering 282 million of those acres – sixty-five percent! — were planted with Monsanto seed.

Many people are coming to believe that such widespread dependence on Monsanto gives the company far too much power not just over US agriculture, but the global food supply as well. That concern is underscored because many of the seeds Monsanto sells are engineered with “terminator” genes that produce plants that are sterile. That means new seeds must be repurchased each year from Monsanto rather than being saved by farmers, an ancient practice that farmers worldwide depend on for the next year’s planting.

The growing fear is that restricting access to the means of food production via sterile seeds could threaten the ability of the world to feed itself, especially in poor, developing countries that are now rapidly switching over to GM crops. According to ISAAA, in 2013 developing countries grew more GM crops than industrial countries did for the second year in a row.  In Latin America, Asia and Africa, farmers collectively grew 54 percent of the GM crops worldwide.

With global influence like that, it’s no wonder that up to two million protesters in 436 cities and 52 countries took to the streets in May 2013 for the first global “March Against Monsanto.” Although people in European countries have turned out by the hundreds of thousands to protest GMOs for decades, it was the largest anti-GMO protest in US history.  But hopefully that was just the beginning.

Another global March Against Monsanto is scheduled for this coming May 24, and this time there’s even greater urgency and consequences for American consumers. Later this year, the US Food and Drug Administration is widely expected to approve the commercial sale of a genetically modified fish, the AquAdvantage salmon, which has been engineered to grow twice as fast as a regular salmon. It is likely to become the first transgenic food animal approved for human consumption.

Environmental groups say it could literally wipe out the world’s native salmon populations if it escapes from fish farms into the wild.  And oh, it won’t have to be labeled so you won’t even know you’re eating a frankenfish.

Sixty-four countries – including the European Union, Brazil, Australia, Japan and China — require foods containing GMOs to be specifically labeled, but not the United States. The FDA doesn’t recognize any difference between GM and non-GM plants or animals, and it maintains that labeling is not necessary because GM foods have the same essential characteristics of nutrition and composition as their non-GM counterparts.

Even though legislation to require labeling in California and Washington narrowly failed in 2012 and 2013 respectively (thanks to $70 million in ads from the biotech and processed food industries), a 2013 poll by The New York Times showed that an overwhelming 93 percent of Americans want GMO foods to be labeled.

Publicity about the FDA’s pending GM salmon approval has ignited a fire under the anti-GMO movement here, and more than three dozen states are frantically working to get mandatory labeling initiatives on this year’s ballot in anticipation of the frankenfish’s arrival.

In the meantime though, with 80 percent of the American food supply containing GMOs the only way to be sure that your food is not genetically modified is to buy organic or look for certification labels from the Non-GMO Project.

The flyer for the March Against Monsanto on May 24 describes the event as, “a global call to action aimed at informing the public, calling into question long-term health risks of genetically modified foods and demanding that GMO products be labeled so that consumers can make informed decisions.”

It’s time to march against this madness.