The president of the National Corn Growers Association is voicing strong opposition to Bayer’s request for tariffs on glyphosate imports from China, saying the move could significantly increase costs for American farmers during an already challenging economic period.

Earlier this week, Bayer and its subsidiary Monsanto filed a petition with the U.S. International Trade Commission and the U.S. Department of Commerce seeking anti-dumping and countervailing duties on glyphosate imported from China. The company alleges Chinese manufacturers have been selling the herbicide in the U.S. at unfairly low prices.

National Corn Growers Association President Jed Bower said the proposed duties would likely drive up the cost of generic glyphosate products that many farmers rely on for weed control.

Bower said the request came as a surprise to many producers, adding that growers feel disappointed by the action at a time when many are facing one of the most difficult farm economies in years.

If the petition moves forward, federal agencies are expected to conduct a formal review that could include public hearings, written comments and in-person testimony before a final decision is made.

The filing comes just one day after President Donald Trump signed an executive order suspending countervailing duties on phosphate fertilizer imports, a move intended to help reduce input costs for U.S. farmers.