On April 7, 2014, the U.S. Court of Appeals for the District of Columbia Circuit heard oral arguments in Monroe Energy, LLC v. EPA (No. 13-1265). In the case, Monroe Energy, a subsidiary of Delta Airlines, the American Petroleum Institute (API), and the American Fuel & Petrochemical Manufacturers (AFPM) are challenging EPA's final 2013 RFS rule. The plaintiffs' arguments include that the rule should be overturned because EPA improperly considered the availability of carryover Renewable Identification Numbers and illegally issued the rule in final nine months after the statutory deadline to do so.

Several large biofuels trade associations intervened in the case on behalf of EPA, including the Biotechnology Industry Organization, Renewable Fuels Association, Growth Energy, and the National Biodiesel Board. They asked the court to uphold the 2013 RFS rule, but to not address the bounds of EPA's discretion to reduce RFS volume requirements due to concerns related to the E10 "blendwall."

Plaintiffs have asked the court for an expedited ruling before the June 30, 2014, compliance deadline for the 2013 RFS requirements.