Corn declined to a three-year low in Chicago last week as analysts said demand for the crop used to make ethanol may shrink if the government scales back the biofuel mandate.

The Environmental Protection Agency is considering a cut in the mandate on the use of corn-based ethanol in 2014, according to an internal proposal provided to Bloomberg News last week. The agency would call for the use of 13 billion gallons, down from 13.8 billion gallons this year, according to the proposal.

A reduction in the mandate will be "negative" for corn, Luke Mathews, a commodity strategist at Commonwealth Bank of Australia, told Bloomberg last week.

Corn for delivery in December closed...