Mexican President Andrés Manuel López Obrador is throwing down the gauntlet when it comes to corn, pitting food sovereignty against the country’s trade agreements.

His proposed ban on genetically modified corn has upset U.S. corn farmers, trade groups and officials and has prompted the U.S. to establish a third party dispute panel to help resolve the disagreement. And yet, López Obrador gives no signs of backing off — making it clear he believes corn, or maize, is a cultural touchstone worth fighting for.

“We will continue campaigning against junk foods that affect our health, including GMO corn,” López Obrador said in a speech given in Spanish earlier this year. “We must first take care of our health and protect native corn varieties.”

Mexico is considered the birthplace of maize, which is still the most extensive crop grown in the country. There are dozens of native corn varieties and many efforts in place to protect them. “Sin Maíz No Hay País,” which translates to “Without Corn, There Is No Country,” is a campaign and phrase used to garner support for protecting native corn varieties.

“Corn is quintessentially Mexican,” said Diego Marroquín Bitar, a fellow for the U.S.-Mexico Foundation, a non-profit that promotes trade between the two countries. “It plays a really important role in the construction of the Mexican identity, and I think that’s where the president comes from.”

López Obrador recently released a revised draft of Mexico’s national food production standard, stipulating that no genetically modified white corn is to be used in corn dough, or masa, for tortillas and tostadas.