Grown only on the slopes of two volcanoes on the Big Island of Hawaii, kona remains one of the better-known geographical sources of coffee in the US, even as coffee from Central America and East Africa have become trendier. But kona is still extremely expensive—when it’s real.

Three kona farmers, reports West Hawaii Today, are suing several huge retailers and multiple coffee producers for selling fake kona coffee. The list of defendants includes Walmart, Amazon, Costco, Safeway, and Kroger, along with producers like Maui Coffee Co (Hawaii), Magnum Coffee Roastery (Michigan), and Copper Moon Coffee (Indiana).

Kona coffee isn’t a type of roast, like French or Italian; it specifically refers to coffee grown in these two locations. Because of the small land area it’s grown on, as well as the fact that kona growers are subject to more stringent American labor laws, kona coffee tends to cost more than twice as much as coffee grown elsewhere. Only 2.7 million pounds of kona coffee are produced each year. But the laws regarding who can call their product “kona” are not helpful.

Because kona is so expensive, producers often sell “kona blends,” meaning kona mixed with non-kona coffee, to reduce costs (or theoretically produce different flavors). Hawaiian state law says that any “kona blend” coffee sold in Hawaii must contain at least 10 percent kona, and must state the precise percentage of kona in the blend. There is no corresponding federal law, meaning that “kona blends” may contain hardly any kona at all. (There was also a case, settled in 2013, of a “kona blend” that contained zero kona coffee.)

Over the past few years, testing has evolved to allow the identification of individual coffee beans with a high degree of certainty. Last week, kona farmers filed a class action lawsuit, along with the results of testing showing, they say, that 19 “kona” products contained either only trace quantities of kona or none at all. This, they say, hurts both the kona name and their individual businesses.

According to the National Law Review, the plaintiffs will have to prove that the labeling is false, which is why the chemical testing is so vital. The lawsuit was filed in a federal court in Seattle.