Iowa Senator Chuck Grassley sent a letter to Attorney General Merrick Garland calling for the Department of Justice to investigate the fertilizer industry. He says farmers are raising concerns about possible U.S. antitrust law violations and market manipulation and it needs to be explored.

He’s not sure if DOJ will uncover wrongdoing but says plenty of farmers and organizations believe fertilizer companies are colluding and unfairly raising the price of their products.

Grassley says an investigation is a longer term solution but there are more immediate remedies including getting the International Trade Commission to lift their tariffs on phosphate imports for one.

Grassley writes in his letter that agriculture 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.