Vegan mayonnaise—which by definition doesn’t contain eggs—can’t be marketed as mayonnaise, according to the Food and Drug Administration.

Hampton Creek Foods, Inc., a health foods company whose best known product is a vegan, egg-free mayonnaise called Just Mayo, was sent a warning letter from the FDA on Aug. 12.

“According to the standard of identity for mayonnaise, egg is a required ingredient,” said the letter, which was released Tuesday and was signed by William A. Cornell, Jr., the FDA’s director of the office of compliance. “[H]owever, based on the ingredient information on the labels, these products do not contain eggs. We also note that these products contain additional ingredients that are not permitted by the standard, such as modified food starch, pea protein, and beta-carotene, which may be used to impart color simulating egg yolk. Therefore, these products do not conform to the standard for mayonnaise.”

The FDA requires that a product calling itself “mayonnaise” contain at least 65% vegetable oil and have one or more “egg yolk-containing” ingredients.

The “egg” of Hampton Creek’s Just Mayo—and Just Mayo Sriracha, which was also cited in the warning letter—is actually a byproduct of Canadian yellow pea and has fast become a popular product on grocery store shelves across the country, TIME reported last year. The company boasts investors that read like the who’s who of the tech world: Bill Gates, Peter Theil and Vinod Khosla all back the San Francisco-based company.

But in November 2014, Unilever—which owns Hellmann’s Real Mayonnaise—filed a lawsuit against Hampton Creek, arguing the lack of eggs in its Just Mayo disqualifies the product from being classified as a mayonnaise. Unilever dropped the suit less than a month later, with a company spokesperson saying in a statement, “We believe Hampton Creek will take the appropriate steps in labeling its products going forward.”

The letter from the FDA also takes issue with Hampton Creek’s claim that Just Mayo is “cholesterol free,” as well as the website tagline “You’ll never find cholesterol in our products,” saying that “it is an unauthorized synonym for ‘cholesterol free.'”

The FDA has asked Hampton Creek to respond within 15 business days of receiving the letter. Hampton Creek has yet to do so, and did not immediately respond to TIME’s request for comment.

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Write to Tanya Basu at tanya.basu@time.com.