It’s heartwarming when a brand uses its scale in the interest of the public good. It’s better still when its impact is so massive it changes harmful laws.

French grocery chain Carrefour accomplished just that, and in a deliciously subversive way, by launching the “Black Supermarket” alongside agency Marcel.

Activated at Carrefour stores nationwide, the campaign sold illegal cereals, fruits and vegetables in a suitably “black market” context.

The “Black Supermarket” project was an attack on Europe’s Official Catalogue of Authorized Species, which “dictates which seeds are eligible for sale and cultivation,” Marcel’s creative director, Gaëtan du Peloux, explained. “In Europe, as it is the case almost all over the world, people have access to only three percent of existing cereals, vegetables and fruits. The other 97 percent—2 million farmers’ seed varieties—are illegal.”

The Official Catalogue of Authorized Species was originally conceived with good intentions: guaranteeing food safety for everyone in the European Union.

“Since then, its mission has been perverted,” du Peloux said. “Little by little, the agrochemical lobby had the catalogue rules changed so that only hybrid seeds could be eligible. In 1981, they passed a law to prohibit the sale of anything that did not fit into the catalogue. Today, it no longer serves food safety; it serves business.”

Infringement of these laws can result in fines that can bankrupt an honest farmer, not to mention the cost to distributors who work with them.

“As a result, 90 percent of farmable varieties have disappeared worldwide in the 20th century [according to the U.N.’s Food and Agriculture Organization], farmers have to depend on pricey hybrids patented by the agrochemical industry, and consumers are deprived from a wide range of superior produces, richer in nutrients, taste, and better for the environment,” du Peloux said. “It’s a disaster for biodiversity, taste, and health.”

It sometimes feels like our futures have been taken hostage by forces larger than ourselves. The name “Monsanto” evokes just such an emotion—one example of a brand that’s made it nearly impossible for farmers to grow crops that haven’t been genetically engineered.

Sometimes, though, we’re also reminded that the market rewards positive social forces when an execution resonates just enough to hack whole communities.

In 1996, Carrefour became the first major retailer to forbid GMOs in stores. Since then, it’s become the largest organic products retailer in France. The purpose of its Black Supermarkets was to give this positioning more visibility and reposition “illegal” producers as national heroes.

The Black Supermarkets launched last year on Sept. 19, headlined by an “illegal dinner” that ran concurrently with the French National Food Forum, putting Carrefour itself at risk for heavy fines.

On Sept. 20, Black Supermarkets opened nationwide and 600 forbidden varietals were staged in massive herbariums, over which hung the faces of illegal producers who had been sued by agrochemical lobbies. An accompanying web film also spread the word, reinforced by print and outdoor executions.

“[People] bought the illegal goods en masse—our maximum of 70 tons, due to scarce illegal supply,” du Peloux said. Visitors were also asked to sign a Change.org petition to change the law, resulting in over 85,000 signatures.

Carrefour signed five-year supply contracts with illegal producers and invited opinion leaders to witness the act.

The brand claims this is the first time a retailer has broken the law in order to change it.

“Carrefour sees its leadership position as a responsibility to advance food quality for everyone,” du Peloux said. “But the main barrier to food quality in France is not the competitors [nor] consumers’ behavior; no, it is the law. So we came up with the idea that, to change the law, maybe Carrefour had to defy it.”

In terms of why he feels the Black Supermarket made such an impact, he added, “This is the first time a brand of such importance and power outlawed itself for a good cause. … After 40 years of prohibition, dozens of draft laws to re-authorize farmers’ seeds had already been rejected.”

The media remained indifferent. “To impact European politics, we knew we had to take a risk: expose this aberration to all and rally consumers and the media,” du Peloux said. “People were baffled to discover this absurd law. They joined the cause, even the worst critics of the retail industry. The fact that a big retail leader defied the law struck public opinion enough to change it.”

He also called Black Supermarket “an action that resonates with our times.”

“We are at a time when people think governments no longer have the power to change the world, but think corporations do,” he said. “They expect businesses to advance societal interests while taking care to cause no harm to our shared environment and community. It gives a new role to corporations, especially big corporations, which have greater lobbying power and responsibility. That’s why Carrefour’s actions had such an echo.”

Over the course of the National Food Forum, the Black Supermarkets generated over 300 million media impressions—69 percent of which were online, driving people to the petition.

In-store traffic rose 15 percent, with the produce section benefiting from a sales bump of 10 percent. It also led to an 8 percent rise in positive brand sentiment toward Carrefour, lifting its score from 65 percent to 73 percent.

More importantly, on April 19, the European Parliament ratified a new organic agriculture regulation, reauthorizing the sale and cultivation of farmers’ seeds.

It isn’t just a win for Carrefour and the EU community; it sends a strong message to agencies.

“We truly believe that we are in the right place to push clients to achieve great things for our common future, simply because that’s what people expect from brands and because brands really do have this power,” du Peloux said.