MEXICO CITY, MEXICO — Mexico’s president said he will sign an agreement with tortilla makers that ensures only non-genetically modified (GM) white corn is used to make the country’s food staple and sets new tariffs on imports of the grain, Reuters reported.

President Andres Manuel Lopez Obrador said tariffs will promote more domestic purchases and hailed the agreement’s assurance that only white, non-GM corn varieties would be used in tortillas.

He has taken exception with traces of GM corn that have shown up in relatively small white corn imports from South Africa, Reuters reported. Lopez Obrador told reporters that they have proof of the GM traces.

Mexico is mostly self-sufficient in white corn but imports a large amount of yellow corn for use in animal feed.

The nation is in the midst of a trade dispute with the United States over a presidential decree to limit the use of GM corn, particularly for human consumption.

The United States and Canada requested dispute settlement consultations with Mexico under the United States-Mexico-Canada Agreement (USMCA) saying the decree is not based on science and would disrupt US exports to Mexico.

Mexico imports about 17 million tonnes of corn from the United States, most of which is yellow corn. About 5% of that total from the United States is white corn.