Last week Subway, the world’s biggest fast food chain, became the latest in the industry to announce it was adopting a stronger antibiotic-free policy—serving chicken and turkey raised without medicines intended to fight bacterial infections starting next year. The announcement came shortly before a petition with hundreds of thousands of signatures was about to be delivered to Subway’s headquarters in Connecticut calling for an end to antibiotic use in the sandwich maker’s food supply chain. More and more restaurant chains and food production companies are taking action against antibiotic overuse, in large part due to public demand. Although the trend started with Chipotle and Panera Bread, fast-food giants such as McDonald’s and Chik-fil-A are also making the switch. As more large food chains commit to antibiotic-free policies, suppliers will be forced to adopt new practices or lose vital sales.

Overusing antibiotics can lead to bacteria that are resistant to treatment. Limiting antibiotic use to when it is strictly necessary—in humans as well as in animals—is vital in order to ensure their continued efficacy. That’s why advocacy groups, wielding massive petitions, had been calling for Subway to stop using meat from suppliers that raised their animals with routine antibiotics and rely instead on what they referred to as antibiotic-free livestock.

But the term antibiotic-free is a bit of a misnomer. According to Bill Wenzel, Antibiotics Program director at the U.S. Public Interest Research Group, the PIRG is not calling for a total ban on antibiotics, which are at times necessary to treat sick animals. What the group seeks to eliminate is the routine overuse of antibiotics for growth promotion or wide-scale disease prevention. Routine use of antibiotics is mainly seen in large-scale farming operations, where animals are kept in close, confined areas that often become breeding grounds for transmitting illnesses. Addressing the routine use of antibiotics—mainly seen with cattle and pigs—thus requires a change in farming practices.

When it comes to taking action against antibiotic overuse, efforts in the marketplace have been much more effective than tackling the government. The U.S. Food and Drug Administration has guidelines in place that seek to restrict the routine use of antibiotics. Adopting those guidelines is voluntary, however. “One of the things that was frustrating to us was that we couldn’t move the Congress or the president to substantial action to take care of the public health threat,” Wenzel says.

Three states attempted to pass bills that would enact state-level policies. In Oregon and Maryland neither bill was voted into law. California is the one notable exception. Earlier this month the state signed into law legislation banning the use of antibiotics not prescribed by a veterinarian, including routine antibiotics for disease prevention. “Our hope is that now that California has proven that it can be done, other states will take up the charge as well,” says Lena Brook, a food policy advocate at the Natural Resources Defense Council. The NRDC, along with PIRG, were two of the advocacy groups who planned to deliver the petition with nearly 300,000 signatures to Subway.

Consumers have already demonstrated the ability to change company policy. “Collectively, the companies are ahead of where the federal government is on this issue,” Brook says. “The marketplace is leading the charge.”

Chipotle in 2001 and Panera Bread in 2004 became the first restaurant chains to commit to sourcing some of their meat from antibiotic-free livestock. Other major chains, however, including McDonalds and Chick-fil-A, are beginning to take action as well, particularly in regards to sourcing poultry. This is partly because three major poultry producers—Tyson Foods, Purdue Farms and Pilgrim’s Pride—have all taken measures to reduce the amount of medically unnecessary antibiotics used. “Chicken is the low-hanging fruit in this scenario,” Brook says. For restaurants, making the switch to antibiotic-free beef and pork is where the real difficulty lies, because there’s so much less available.

Subway plans to switch to antibiotic-free beef and pork by 2025. Its biggest challenge will be securing a steady supplier that can meet both its standards and its demand for meat.

Restaurant chains taking such actions cause an industry-wide domino effect due to their power in the marketplace. “Larger restaurant chains deal with so much volume that having them put strict requirements in place affects change,” Wenzel says. Those requirements put financial pressure on farmers and food producers, unlike the voluntary guidelines set by the FDA. In order to continue doing business with major buyers, meat suppliers will have to follow requirements regarding antibiotics—although they have a few years to implement those changes.