The organization is fighting to keep Chile’s model from being adopted more widely. Roger Lowe, a spokesman for the group — whose board members include executives from Coca-Cola, PepsiCo and Mondelez International, which owns brands like Oreos, Chips Ahoy and Ritz crackers — said it was concerned about the “evidence and impact” of Chile’s laws.

Emily Davis, a spokeswoman for the United States Trade Representative, said she could not comment on what she called “alleged negotiating documents.” In general, she said, “the United States supports science-based labeling that is truthful and not misleading.”

Proponents of more explicit labels said the Trump administration’s proposal and the corporate pressure behind it hold the potential to handcuff public health interests for decades.

“It is one of the most invasive forms of industrial interference we have seen,” said Alejandro Calvillo, the founder of El Poder del Consumidor, or Consumer Power, a health advocacy group in Mexico that was illegally targeted with government spyware when it fought for a soda tax in Mexico. “The collusion between the industry and the government is not only at the level of spying — it reaches the level of the renegotiation of Nafta and the nation’s own policy against obesity.”

The American proposal conflicts with the guidance from Mexico’s national health institute and from the World Health Organization. Both have recommended that Mexico pass regulations to help combat diabetes, which claims 80,000 lives a year there. That is one of the highest rates in the world — and more than double the record number of homicides in the nation in 2017.

Mexico’s Ministry of Health, which is directly involved in the trade negotiations, said it was reviewing the American proposal with the nation’s health authorities.