The United States has previously threatened a trade dispute panel under the trilateral agreement with Canada and Mexico (TMEC) over the plan, which would ban genetically modified corn for human consumption.
Mexico has said it believes the disagreement with Washington is politically motivated.
US Agriculture Secretary Tom Vilsack had said a panel on trade disputes under the free trade agreement would be the next step if the talks were unsuccessful.
USTR head Katherine Tai held talks with Mexican economy secretary Raquel Buenrostro on the issue late last month.
Corn for food use comprises around 21% of Mexican imports of the cereal from its northern neighbor, according to a representative of the National Corn Growers Association, citing data from the United States Grain Council.