Mexican health safety regulators have denied a permit for the import of a new strain of GMO corn, Reuters reports. It’s never been legal to grow genetically modified corn in the country, but Mexico imports about 16 million tons of corn per year from the United States, almost all of it GMO, so this could be significant. Mexican regulators declined to approve the new variety due to concerns that glyphosate, one of the herbicides sprayed on GMO crops, might pose health risks to humans. (Bayer, a company that sells GMO corn seeds, has always argued that glyphosate does not cause cancer, and global regulators have tended to agree, but the company also spent billions settling lawsuits that argue the opposite). The regulatory decision is consistent with President Lopez Obrador’s goal of banning glyphosate and GMO corn for human consumption throughout Mexico by 2024. There’s a lot going on here, but here’s why it matters: Mexico is basically saying “no” to importing new products sprayed with glyphosate, a move that’s sure to piss off some U.S. agribusinesses, which rely heavily on the chemical. U.S. companies will likely argue the decision is protectionist (because it keeps U.S. corn out of the market, possibly creating more favorable conditions for local growers) and inconsistent with past policy (because Mexico has previously approved the import of about 90 GMO corn varieties). One further wrinkle: Mexican farm groups claim the decision violates a major trade agreement. It’ll be interesting to see how this plays out.