Well actually, a lack of eggs.

Unilever subsidiary Conopco has filed a civil suit in New Jersey federal court against Hampton Creek, alleging false advertising and unfair competition. It claims that because Hampton Creek’s Just Mayo product doesn’t contain any eggs, it shouldn’t be called or marketed as mayo or mayonnaise.

“Despite its name, Just Mayo does not contain just mayonnaise,” reads the complaint. “In fact it is not mayonnaise at all. Rather, it is a plant-based vegan alternative to real mayonnaise.”

Hampton Creek’s Just Mayo competes with Unilever’s Best Foods and Hellmann’s brands. The claim acknowledges that Just Mayo is stealing market share from Hellmann’s.

The civil action alleges that Just Mayo neither tastes like nor binds ingredients and sauces together the way mayo should. That, along with what it calls “unsubstantiated superiority claims” have “caused consumer deception and serious, irreparable harm to Unilever and to the product category the industry has taken great care to define in a way consistent with consumer expectations.”

In addition to damages, Unilever is seeking an injunction against Hampton Creek, which would keep the company from calling its product mayonnaise, marketing it as superior to Unilever’s brands, and ultimately forcing it to withdraw anything with Just Mayo branding from the market.

Hampton Creek CEO Josh Tetrick says that he does not believe that the company is in violation of what’s called “the standard of identity” for mayonnaise and plans to fight it. But he also thinks the lawsuit is an opportunity to make a larger point. “This is a conversation around how this system of food needs to be rethought,” he says. “You’ve got to make it easier for innovators to innovate and for people to eat in a way that’s ultimately better.”

Tetrick thinks that Hampton Creek—which is focused on making plant-based products to improve the food system—will likely be the target of other lawsuits as it branches into new products. “It’s just kind of the nature of change,” he says.

Vegan products branded as mayo that pre-date Hampton Creek are on the market, but those offerings are more clearly targeting health-conscious consumers. Tetrick has made a point of going after a larger demographic with Just Mayo, selling his product not just in the Whole Foods of the world but also the Wal-Marts. The company has historically downplayed that Just Mayo is vegan in order to appeal to a broader population. That also makes the product more of a direct threat to Unilever.

Tetrick shared an email with Fortune that he received from Unilever’s Global VP of marketing only days after the suit was filed. It read: “Love what you are doing…Very much in line with our Unilever Project Sunlight #brightfuture philosophy.”

Tetrick made his debut appearance on Fortune’s 40 Under 40 list earlier this year.

Unilever has not responded to requests for comment. We’ll update if they do.