Speculators in the agricultural commodities markets are forcing grocery prices to rise too quickly and erratically, according to some top economists marking World Food Day on Sunday.

“Excessive financial speculation is contributing to increasing volatility and record food prices, exacerbating global hunger and poverty,” wrote 461 economists, from more than 40 countries, in an open letter

They called upon the U.S. Commodity Futures Trading Commission to crack down on speculators who have been buying large amounts of corn, wheat, soy and other commodities, hoping to make a profit. The economists argue that increased trading is a significant part of the reason grocery prices are higher this year.