Plum-pox resistant plumsPublic DomainLike it or not—and I’m in the not camp—a mandatory, uniform national GMO labeling scheme appears increasingly likely.

A number of factors make that so. On the one hand, activists who support mandatory labeling of GMO crops and foods containing GMO ingredients have gained a minor toehold in the states. While Connecticut passed a first-in-the-nation mandatory labeling law earlier this year that has little more than a snowball’s chance in hell of ever taking effect, a Washington State ballot measure appears likely to pass next month.

But hold on a minute. There’s a good case to make that both the Connecticut law and the looming one in Washington State are unconstitutional. Meanwhile, President Obama promised before his first term to push for mandatory GMO labeling, but has done nothing of the sort while in office. And there’s also no major push in Congress to pass a federal GMO labeling law. As recently as June I was also  quoted as saying that mandatory GMO labeling was hardly inevitable.

So why am I increasingly confident now that some federal mandatory GMO labeling law will materialize?

Because of what’s happening on the other side of the debate. Major players on the business side, including Walmart, America’s leading grocer, and General Mills, which bills itself as “one of the world's largest food companies,” have publicly tipped their hands that they’d support some sort of mandatory labeling.

As I noted this summer, Walmart held a meeting with FDA officials and others from the food industry earlier this year where, it was alleged, the grocer and other food sellers that have opposed state labeling requirements would push for the federal government to adopt a national GMO labeling standard.

And just last week, Ken Powell, the CEO of General Mills, announced at the company's annual stockholders' meeting that the company “strongly support[s] a national, federal labeling solution.”

Powell’s comments are a game changer.

But do they mean that anti-GMO activists and food companies are on the same page? Not by a longshot. Powell made clear in his remarks that the company supports “a national standard that would label foods that don’t have genetically engineered ingredients in them, rather than foods that do.” (emphasis mine)

I suspect that anti-GMO activists would hate that solution because it wouldn't provide the "information" they want and because all of the significant testing and labeling costs of the mandatory scheme Powell suggests—along with any liability for not testing GMO-free foods or for mislabeling—would be borne by the GMO-free farmers and food producers they frequent (and by their customers, in the form of higher prices).

But Powell's plan isn't likely to take hold. In fact, I suspect Powell is posturing—at least in part.

He’s doing so to ensure that any national labeling system that arises will resemble nothing that longtime supporters of mandatory labeling have been pushing for. Why? It’s all due to the dreaded “c” word: compromise.

In light of Powell's comments, here’s what I think a mandatory federal GMO labeling compromise would look like: Congress will propose a bill that would require all food to be labeled either one of two ways—as containing GMOs (what the activists want) or as free of GMOs (what Powell suggests). In other words, any and every food product sold in this country would have to disclose on its label something like either "Contains GMO Ingredients" or "Contains No GMO Ingredients."

Anti-GMO activists may consider a compromise like this to be a victory. But they should take a closer look. The downsides of this compromise would be enormous for their cause.

For one thing, testing and labeling costs would be substantial for both sides. But how will a small farmer who has to pay to test crops she grows and packages stay in business? Or how about the small canner or grocer that buys her produce? Meanwhile, economies of scale assure that such a compromise won't impact large producers nearly as much.

Furthermore, producers and sellers of food that "Contains No GMOs" would have to test all of their food (to prove the negative). And they’d be sued time and time again if they don't test, if a test result proved false, or if they simply made an honest mistake on a label. Meanwhile, if a company knows it’s producing or selling GMO food, its costs are comparatively small to put a "Contains GMOs" label on its products.

But whether the costs borne by GMO and GMO-free producers would be a lot higher or only slightly higher, the logical outcome of this compromise would be that all of our food would cost more. And the benefits to consumers would be nonexistent.

Of course, consumers would "know" what's in their food—a key goal claimed by GMO opponents. But they should know this too: the result of the compromise would likely be more GMO food choices and less GMO-free food choices.

Unfortunately, the potential unintended consequences of this federal labeling scheme are so terrible and obvious that they appear to make for the perfect Washington compromise.

Not everyone agrees with my theory about a coming federal GMO labeling compromise.

"The only way industry will agree to federal labeling is if it’s watered down, essentially meaningless and preempts states from going further," says public-health lawyer Michele Simon, president of Eat Drink Politics, who supports mandatory GMO labeling and who wrote about GMO preemption earlier this year.

I think Simon is right about preemption. But I also think her preemption theory fits snugly alongside my own theory. The federal compromise I suggest may happen would also almost certainly preempt states—whether explicitly or implicitly—from adopting their own GMO labeling schemes.

I’m personally and professionally indifferent to choices by farmers and other producers, food sellers, and consumers between GMO foods and non-GMO foods. But I’m also fiercely opposed to laws that limit or skew their right to make the diverse food choices they want.

It’s why I’ve opposed mandatory GMO labeling and cheered voluntary labeling. It’s why I argued adamantly against the so-called “Monsanto Protection Act.” And it’s why I’m warning here against what I fear is a looming and foolhardy federal compromise on mandatory GMO labeling.