Senate Republicans want the Environmental Protection Agency to consider waiving the country’s ethanol production mandate amid rising food prices.

Twenty-two Republican senators, including presidential candidate Sen. John McCain of Arizona, have sent a letter to the EPA. They said the agency has the authority to waive, or restructure, a law passed by Congress requiring a five-fold increase in U.S. ethanol production by 2022.

Lawmakers are ramping up questions about the potential unintended consequences of using corn for fuel amid rising global demand for food.

Shares of VeraSun Energy Corp. fell 12 cents, or 1.75 percent, to $6.75.