NAFTA, as is well known by now, has had "winners" and "losers" on both sides on the border.
Here is an exceptionally noteworthy article by Timothy Wise of Tufts University on the article of U.S. dumping of agricultural products in Mexico, originally published in NACLA Report of the Americas.
Some highlights:
* "Mexican farmers on average lost more than $1 billion per year during the nine-year period of 1997–2005, with more than half the losses suffered by the country’s embattled corn farmers"
* "Without exception, the United States exported {agricultural] products at prices below what it cost to produce them, one of the definitions of dumping under World Trade Organization rules."
* "The losses from U.S. dumping surpass the total value of Mexico’s annual tomato exports to the United States, widely touted as Mexico’s biggest NAFTA success story in agriculture."
I also highly recommend Wise's other excellent works, such as the co-written Rethinking Trade Policy for Development: Lessons From Mexico Under NAFTA, available directly as pdf here, as well as the new study Subsidizing Inequality: Mexican Corn Policy Since NAFTA, available here in English and here in Spanish.