Senator Armando Rios introduced a bill that would drastically cut down Mexico's purchases of U.S. corn.
Mexico bought nearly 25% of all U.S. corn last year, totaling $2.6 billion. It's the second biggest market in the world for U.S. corn only behind Japan.
Trump says NAFTA, the free trade deal with Mexico and Canada, has been a "one-sided deal" in which Mexico has won and America has lost.
"The position of Donald Trump is a mistaken one and it's a lying one," Rios told CNNMoney Wednesday. "They have been insisting that Mexico takes advantage of the U.S. regarding NAFTA and that's totally false... It's a big lie, so there is a good way to show that this is not true."
That way would be to cut off imports of U.S. corn. In his bill, Rios says Mexico would reduce its imports of U.S. corn by 60% in the first year, 80% in the second and 100% by the third year.
The bill's chances of becoming law are unclear, but Rios said that the bill already has the support of several senators from political parties that control Mexico's Congress.