Three consumer groups are suing General Mills for calling the oats in its Nature Valley granola bars “100% natural,” the latest in a rash of labeling lawsuits against food companies.

Organic Consumers Association, Moms Across America and Beyond Pesticides filed class action complaints in U.S. District Courts in Minnesota, California and New York against the Golden Valley-based food company this week.

The groups allege that 0.45 parts per million of glyphosate, a commonly used herbicide, were detected in the bars. While that is significantly below the 30 parts per million maximum recommended by the U.S. Environmental Protection Agency, the plaintiffs argue it falls outside what most consumers deem natural.

This isn’t the first time General Mills has been sued for using the term on its Nature Valley products. The company settled a lawsuit in 2014 and, not while admitting wrongdoing, agreed it would not use the 100 percent natural label on products that contained high-fructose corn syrup, maltodextrin or other highly processed ingredients.

General Mills is not commenting on the litigation but said in a statement, “We stand behind our products and the accuracy of our labels.”

What classifies as “natural” has not defined by the U.S. Food and Drug Administration, apart from natural colors and flavors.

“The case again highlights the fact that there is no consensus working definition yet of what ‘natural’ means. This has been, and remains, a major problem,” said Dick Wegener, a lawyer specializing in food labeling at Faegre Baker Daniels.

The term can virtually mean anything, but the plaintiffs argue consumers have certain expectations when they see a “natural” label.

The suit alleges that use of this phrase on several Nature Valley products is misleading and deceptive, arguing that “no reasonable consumer, seeing these representations, would expect that the oats or any ingredients in the products to contain something that is unnatural.”

In the spring, the FDA requested public comments on what “natural” should mean, indicating the agency’s intention of creating a definition for the label.