Vegans, be wary. The FDA has warned the makers of the product Just Mayo that they cannot use the name “mayonnaise” without adding eggs to their recipe.

FDA rules make it clear that to be defined as mayonnaise, the product must contain 65% vegetable oil and have one or more “egg-yolk-containing” products.   As The Market Business reports, Hampton Creek Foods, Inc, currently manufactures a vegan edible marketed as mayonnaise, but, unsurprisingly, it contains no eggs.

The FDA sent a letter of warning to Hampton on August 12, telling them that the product Just Mayo in fact does not conform to national “standard of identity” for the classification of mayonnaise. Along with the lack of eggs, the FDA pointed out the product contained several other ingredients—modified food starch, pea protein, and beta-carotene—that are not allowed in a mayonnaise product.

Hampton has apparently skirted the issue of food identity before.   Hellmann’s Mayonnaise’s corporate parent, Unilever, sued them in 2014, claiming their Just Mayo was not mayonnaise because of the lack of egg. The suit was dropped as Unilever decided to let the FDA take the charge.

A San Francisco-based company with numerous high-profile technology world backers, Hampton’s classification of their vegan products opens the floor to questioning the world of food substitutions at large. Food companies that sell alternatives must work to skirt the classification of their products in marketing and advertising.

The FDA allowed 15 days for a response to their letter but Hampton has yet to do so.