WASHINGTON — The National Grain and Feed Association today urged Congress to prepare to enact emergency legislation to avert what the organization deems “a potentially calamitous national freight rail strike” that may occur as early as 12:01 a.m. on Dec. 6.

Although President Obama on Oct. 6 established a Presidential Emergency Board and an additional cooling-off period to provide time for the nation’s Class I railroads and unions to reach agreement, the N.G.F.A. said two unions — the Brotherhood of Locomotive Engineers and Trainmen, and the American Train Dispatchers Association — have not agreed to an extension of the cooling-off period. Thirteen unions have reached agreements and one agreed to extend the cooling-off period until Feb. 8, 2012.

“Such a strike — indeed the mere prospect of one as the Dec. 6 deadline approaches — would further imperil an already fragile economic recovery and job market,” the N.G.F.A. said. “It also would have significant adverse impacts on the grain, feed, grain processing and export sectors represented by our membership, which are highly dependent upon freight rail transportation to efficiently and cost-effectively move raw and processed agricultural products to domestic and international markets.”

According to the N.G.F.A., freight railroads account for about 35% of the transportation needs for agricultural products, with demand often peaking during the post-harvest season that is taking place right now. Additionally, the N.G.F.A. said the onset of winter typically means weather-related restrictions soon will be imposed upon barge traffic on the inland waterways, a mode of transport that accounts for about 12% of agricultural product movement.

The N.G.F.A. said, “A national freight rail strike would undermine significantly our industry’s ability to meet domestic and export market demand — U.S. agricultural exports are one of the sole positive contributors to the U.S. balance of trade — and would result in significant adverse financial impacts on a wide array of businesses dependent upon agricultural production. These include food, animal feed, pet food and biofuel firms and other industry sectors that employ millions of Americans. Such a strike also would depress farm-gate prices to agricultural producers.”