Lori Hoag, a spokeswoman for the dairy unit of Monsanto, said her company did provide financial support to Afact. But Ms. Hoag asserted that the group is led by farmers, not Monsanto.

“They make all the governing decisions for their organization,” she said. “Monsanto has nothing to do with that.”

Afact has come together as a growing number of consumers are choosing milk that comes from cows that are not treated with the artificial growth hormone. Even though the Food and Drug Administration has declared the synthetic hormone safe, many other countries have refused to approve it, and there is lingering concern among many consumers about its impact on health and the welfare of cows.

The marketplace has responded, and now everyone from Whole Foods Market to Wal-Mart Stores sells milk that is labeled as coming from cows not treated with the hormone. Some dairy industry veterans say it’s only a matter of time before nearly all of the milk supply comes from cows that weren’t treated with Posilac. According to Monsanto, about a third of the dairy cows in the United States are in herds where Posilac is used.

And the trend might not stop with milk. Kraft is planning to sell cheese labeled as having come from untreated cows.