Currently, winemakers aren’t required to disclose dozens of additives—even those that mean a bottle is no longer vegetarian or vegan.

What’s in your wine? When you pick up a bottle of California Cabernet Sauvignon, you’ll likely assume the obvious: That’s it’s made entirely from fermented Cabernet Sauvignon grapes. Well, not only does U.S. law allow wineries to use up to 25 percent of grape varieties other than what’s on the label without having to declare it, the law also allows for 62 additives that can be used in wine without these ingredients being disclosed anywhere on the bottle.

Though all of these additives are considered harmless, some of them might raise an eyebrow for other reasons. For instance, MegaPurple, which is made from grape juice concentrate, can be added to wines to enhance color, a controversial step some in the wine world equate to a kind of cheating. But potentially even more troublesome are ingredients like isinglass, made from fish bladders, and egg whites—both of which are used to help clarify wine, and both of which can quietly keep a wine from being vegetarian- and vegan-friendly.

Isabelle Legeron, who in 2004 became France’s first woman to receive the prestigious Master of Wine certification, discussed how adamantly she opposes this practice, which is common around the world, in a recent interview with Forbes. “Somehow there’s a very interesting part of the population of wine drinkers who are extremely savvy in how they shop for food,” she stated during a discussion of different winemaking processes. “They’re really careful in what they consume, and yet they don’t know the bottle they are about to pop open for their birthday is made with a fish derivative, known as fish leather [isinglass]. It’s routinely used in white and sparkling wines. It’s a binding agent. And it’s at the bottom of the vat. There are trace elements left. Milk and egg derivatives are also routinely used, and if I’m a vegan, I wouldn’t want that. In a way we’re still in the dark ages when it comes to the wine industry.”

Legeron, who runs Raw Wine – an organization specifically dedicated to “leading the charge for transparency” – clarified that she’s fine with these ingredients being used, but that drinkers should know about it. “I’m not against the use of these additives,” she later continued. “I don’t think it’s a great idea. But my issue is that we have no idea what we are putting in our bodies. That’s my main problem. People need the choice in what they are drinking.”

So what’s her solution? Instead of trying to change the laws, Legeron encourages people to “start lobbying with our dollars.” Specifically, she said, “We need to not buy a wine if we don’t know how it’s made.” Interestingly enough, around this time two years ago, beer maker Guinness received public backlash after vegans railed against the brewery for using isinglass as a fining agent in its signature stout. As a result, the brand decided to tweak the beer’s 256-year-old recipe to make it vegan. Not to say there’s anything inherently wrong with fish bladders, but it is proof that such grassroots campaigns really can work.