Whole Foods has offered support to small farms and allowed them to make enough to be sustainable. But now that Amazon might push to lower prices and shed the “Whole Paycheck” label, those same farmers are concerned about their future.

At the Straus Family Farm, next to Tomales Bay north of San Francisco, the feed truck that delivers food to nearly 300 dairy cows now runs on electricity generated from cow poop.

That cow poop–normally a source of pollution at a typical dairy, and one of the reasons for the high carbon footprint of an average glass of milk or hunk of cheese–goes in a digester that also generates power for the rest of the dairy. The cattle graze in rotation, helping grasslands store more carbon. Workers are paid well above minimum wage and get free housing. When the nearby Straus Family Creamery delivers the resulting organic milk (also sourced from eight other local farms), it comes in glass bottles that customers can return for reuse.

All of this is part of the farm’s path to responsible production, including a goal to absorb more carbon dioxide than it produces, or be “carbon positive.” It’s the kind of story that customers want to hear. But it also costs more than running a factory farm, where manure-filled lagoons can pollute both local drinking water and the air, worker exploitation and even deaths are common, and where cows might never leave a barn. And it’s the type of system that Straus and other smaller farmers think might become harder to maintain if Amazon succeeds in its attempt to acquire Whole Foods.

If the deal goes through, an Amazon spokesperson tells Fast Company, “We will want Whole Foods to keep doing what it does best, including working with small farms and producers to bring the best natural and organic foods to customers.” But the company has also suggested that it aims to drive down the cost of food and it may replace more expensive products with its own affordable private label brand. While some producers are optimistic about Amazon’s ability to help their brands grow, the focus on lowering prices worries some farmers that are pushing particularly hard to produce food responsibly.

“To support our farms, our prices have to be higher than others,” says Albert Straus, who runs the Straus Family Farm and is the founder and CEO of Straus Family Creamery. At a Whole Foods in Berkeley, California, the Straus Family Creamery milk sells for $3.39 for a quart, plus a deposit for the returnable glass bottle. “Food [in general] is not reflecting the true cost of production, and that system hasn’t worked. So these forces to drive down prices are going to continue the trend of eliminating family farms in rural communities. It’s not a sustainable system in my mind.”