WASHINGTON — A letter from 18 senators urging regulatory clarity on emissions from the processing of feedstocks such as corn and soybeans has received the support of the American Bakers Association.

The senators’ communiqué seeking a clear ruling on biogenic carbon emissions it calls de minimis stressed the economic benefits of an unencumbered path forward for a U.S. bioeconomy valued at $459 billion in 2016 and at risk of being further outpaced by a European Union bioeconomy valued at $688 billion a year earlier.

The A.B.A. said a lack of E.P.A. clarification of the treatment of biogenic carbon emissions vis-à-vis the Clean Air Act has stifled infrastructure and employment investment that would support the U.S. bioeconomy and stimulate the economic growth of rural America.

“This is E.P.A.’s opportunity to clear a pathway for our rural communities to advance both economically and environmentally,” the letter said. It additionally seeks details on the E.P.A.’s collaboration with the U.S. Department of Agriculture on such issues and requested an update by Dec. 2.

The A.B.A. cited the E.P.A.’s expertise in regulating emissions in other sectors.

“Gaining bipartisan support to encourage the E.P.A. to move forward in providing regulatory clarity on the de minimis nature of biogenic carbon emissions is a step in the right direction,” said Robb MacKie, president and chief executive officer of the A.B.A. “The baking sector is encouraged as E.P.A. also regulates other biogenic emissions, such as ethanol from bakeries.”

The senators’ letter also stressed the science behind a lack of evidence that emissions renewable feedstocks contribute to greenhouse gas buildup.

“Multiple scientific studies have sta-ted that the carbon dioxide absorbed during growth and photosynthesis by renewable agricultural feedstocks, such as corn, soybeans and oilseeds, and the carbon dioxide released during the processing, fermentation or combustion of those same feedstocks is more or less equal within a one-year cycle,” the letter said. “This means biogenic carbon emissions from such facilities are not contributing to long-term increases in atmospheric concentrations of greenhouse gases.”

The Corn Refiners Association said E.P.A. clarification was key to jumpstarting agricultural growth.

“We are very pleased that such a strong group of senators is working with the E.P.A. to make this critical regulatory fix a top priority,” said John Bode, president and c.e.o. of the C.R.A. “As the economic gap between rural and urban America continues to widen, it is vital that we continue to seek out solutions that can spur robust bioeconomic development in America’s heartland.”

Five governors wrote a similar letter to the E.P.A. in August encouraging the agency to act on the issue. In supporting the request, the A.B.A. joined its counterparts in the Biogenic CO2 Coalition, which has urged the Environmental Protection Agency to take action on the matter for more than 10 years.

The Biogenic CO2 Coalition is comprised of the following organizations: the A.B.A., the American Farm Bureau Federation, the C.R.A., Enginuity Worldwide, the National Corn Growers Association, the National Cotton Council of America, the National Cottonseed Products Association, the National Oilseed Processors Association and the North American Millers’ Association.

The letter was signed by Senators Deb Fischer, Tammy Duckworth, Pat Roberts, Gary Peters, Kevin Cramer, Tammy Baldwin, Chuck Grassley, Roy Blunt, Jerry Moran, Joni Ernst, Todd Young, Mike Braun, Ben Sasse, Richard Burr, John Thune, John Hoeven, Michael Rounds and Josh Hawley.