When Cindy first tried the Artemisia Anti-Hemorrhage Formula dietary supplements that she purchased on Amazon, she had no reason to suspect that she was eating donkey. A California native and lifelong vegetarian, she assumed that the world’s largest online retailer had vetted the bottle’s claims of being made from “100 percent pure, natural herbs.” But while reading the back of the bottle, she noticed an ingredient she hadn’t seen before: “gelatina nigra.” She googled it, and what she found made her stomach turn.

Every year, millions of donkeys are slaughtered and skinned to make the so-called gelatina nigra found in Cindy’s dietary supplement. More commonly called “ejiao” or “donkey-hide gelatin,” the animal product is made from donkey skin. It’s in such high demand due to its alleged health benefits that it’s decimating the global donkey population and has led to increasingly brutal treatment of the animals, according to a 2019 report by the Donkey Sanctuary, an advocacy organization. A video the organization obtained shows workers in Tanzania bludgeoning donkeys with hammers to meet their slaughter quotas. “It’s not herbal. It’s literally made with donkeys,” says Cindy, who asked to go by only her first name for privacy reasons. “Why would Amazon sell something that cruel?”

While some retailers like Walmart and eBay have committed to drop products that contain ejiao, edible items containing this ingredient are widely for sale on Amazon in spite of multiple petitions asking that it stop selling them. A legal complaint filed in California last week by the law firm Evans & Page on behalf of the Center for Contemporary Equine Studies, a nonprofit, claims Amazon’s continued sale of these donkey-based products is more than distasteful—it may be illegal.

The Center alleges that Amazon’s distribution and sale of ejiao violates an obscure California animal welfare law called the Prohibition of Horse Slaughter and Sale of Horsemeat for Human Consumption Act. The 1998 ballot initiative, known at the time of its passage as Proposition Six, makes the sale of horsemeat for human consumption a crime on the grounds that horses, like dogs and cats, are not food animals and deserve similar protections. The Center is arguing that, under the statute, horsemeat is defined to mean any part of any equine, including donkeys.

For Frank Rothschild, director of the Center for Contemporary Equine Studies, the law is clear: Donkeys are equines, and the sale of ejiao for human consumption in California is illegal. “We are a scientific organization and not in the business of national advocacy. We want the defendants to stop selling ejiao because it’s illegal,” he says. “That’s the law.”

Bruce Wagman, an attorney unaffiliated with the complaint who has practiced animal law in California for 30 years, says that while the center presents a reasonable argument, it’s unclear whether a judge would agree because the law’s wording leaves room for interpretation. “Horsemeat is not really defined in the text of the relevant statute,” he says. “But the spirit of Proposition Six is absolutely to prevent equines, including donkeys, from being slaughtered for people to consume. Period.”