According to court documents, Superior Court Judge Elihu Berle said that coffee companies failed to show that there was not a significant health risk from a carcinogen in coffee.
Acrylamide is one of nearly a thousand chemicals listed in the state's Safe Drinking Water and Toxic Enforcement Act, which was passed in 1986. The environmental safety regulation is more commonly referred to as Proposition 65.
According to ABC News chief medical correspondent Dr. Jennifer Ashton, acrylamide is a by-product that forms in the roasting and baking process.
"When talking about a toxin you need either a very potent toxin or a high frequency or a very large dose and when you're talking about coffee. Obviously, the concern is the high frequency," she said.
So what is Proposition 65?
Prop. 65 was designed to protect the state’s water sources and require businesses to inform consumers about potential exposure to harmful toxins.
The warning signs have become ubiquitous around California, displayed everywhere from gas stations to apartment complexes to water bottles. The nearly a thousand chemicals on the list can be found in common household products, manufacturing and construction or motor vehicle exhaust.
Acrylamide forms when food is cooked or processed at high temperatures. It can be found in "French fries, potato chips, other fried and baked snack foods, roasted asparagus, canned sweet potatoes and pumpkin, canned black olives, roasted nuts, coffee, roasted grain-based coffee substitutes, prune juice, breakfast cereals, crackers, some cookies, bread crusts, and toast," Delson said.
OEHHA developed "safe harbor levels" for exposure to acrylamide that do not require Prop. 65 warnings. "For cancer effects, the significant risk level for acrylamide is 0.2 micrograms per day," Delson said.
Opponents of the regulation feel many small businesses face unfair lawsuits as a result of the law. To counteract that, Prop. 65 was amended in 2013 to outline a specific protocol for how citizens can file complaints against companies.
Businesses who defy Prop. 65 can face fines up to 2,500 per violation per day.