The market for buying and selling breast milk online and through for-profit companies is booming and many experts are worried about what that entails for the health of newborns across the country, The New York Times reports.

Over the past few years, dozens of pharmaceutical factories launched in the United States to buy, process and sell milk from human mothers to address a variety of health concerns. Some firms aim to concentrate breast milk into high-protein products that can be fed to premature infants in hospital intensive care units across the country.

But emerging “milk sharing” websites, such as International Milk Bank and Only the Breast, have allowed users to buy and sell frozen breast milk products online. In addition, breast milk products aren’t just being sold for babies. Businesses have targeted adults to take advantage of  today’s breast milk business boom. Several other new companies hope to eventually market breast milk products to adults as potential treatments for intestinal and infectious issues such as Crohn’s disease.

Until now, many companies in the business donated mothers’ milk to hospitals. As a result, some nonprofit milk banks argue that the new for-profit start-ups could snap up the lion’s share of the breast milk supply. This would make breast milk too expensive for many mothers to buy.

Breastfeeding advocacy groups, particularly those in poor neighborhoods, are upset. “We are deeply concerned that women will be coerced into diverting milk that they would otherwise feed their own babies,” said the Black Mothers’ Breastfeeding Association. (The group voiced its concern in a recent open letter to Medolac Labs, a firm that wanted to buy breast milk from women in Detroit early last year.)

Mother’s milk is in high demand for a reason. For more information about the benefits of breastfeeding, click here.