(NAFB) – Iowa Senator Chuck Grassley sent a letter to Attorney General Garland calling for the Department of Justice to investigate the fertilizer industry.

American farmers are raising concerns about possible anti-competitive activity and market manipulation. Grassley says fertilizer is an essential input for farmers across the country, and without it, crop yields and agricultural productivity would get significantly smaller.

“I have heard numerous concerns from Iowans and member organizations who are concerned that fertilizer companies are colluding and unfairly raising the price of their products,” Grassley writes in the letter.

The industry has seen dramatic growth in prices: nitrogen fertilizer has doubled in price, anhydrous rose by 131 percent, urea by 110 percent, and potash up 120 percent.

“The DOJ should investigate the fertilizer market so farmers across the country can get assurances that there are no violations of U.S. antitrust law in the fertilizer industry,” Grassley says. “Fertilizer tariffs are placing a huge financial burden on farmers.”