(March 17, 5:55 p.m.) Fresh produce companies who export to Mexico could be caught in the middle of a trade dispute touched off by the Obama administration’s decision to discontinue a plan allowing Mexican trucks access to all U.S. highways.

Mexican officials said they will release a list of 90 U.S. products, including agricultural exports, on March 18 that will face immediate tariffs.

The dispute was triggered by Congressional spending bills that eliminated the U.S. Department of Transportation Cross Border Trucking Pilot Program with Mexico, which opened the U.S. to full access by Mexican trucking firms on a trial basis in 2007.

Industry groups warned legislators in December that Mexico would likely retaliate in such a matter.

“We were kind of at risk if we didn’t move forward and make strides with the program,” said Mark Powers, vice president of the Northwest Horticultural Council, Yakima, Wash. “U.S. agriculture was always concerned we would be one of the groups that would be retaliated against because we have been successful in Mexico.”

The issue dates back to 2001, when a North American Free Trade Agreement dispute settlement panel ruled that the U.S. blanket exclusion of Mexican trucking firms violated U.S. obligations under NAFTA. The panel gave Mexico the right to retaliate against imports from the U.S.

The letter, endorsed by the National Potato Council, Northwest Fruit Exporters, Northwest Horticultural Council, the U.S. Apple Association, the Washington Apple Commission and other groups, warned that the disruption of the trial program would “come at considerable cost to U.S. workers, farmers, businesses and consumers.”

If pears are targeted, up to 400,000 boxes of pears originally destined for Mexico through the rest of the season would need to find a home domestically, said Jeff Correa, international marketing director for Pear Bureau Northwest, Milwaukie, Ore.

The value of U.S. apple exports to Mexico totaled $204 million in 2008, pear exports were valued at $72 million, and fresh potato exports were $29 million, according to the U.S. Department of Agriculture.

“We’re hearing this could be an immediate raise in tariffs,” Correa said. “If we’re on that list and if it goes into immediate affect, that basically rolls out the red carpet for Argentine pears in that market, and I imagine all our exports would pretty much cease.”

Whether Mexico follows through with its announced intention of tariffs remains to be seen, but disagreements between the U.S. and its biggest trading partner are closely watched by exporters.

“They’re interested in making their concern known,” said Rebecca Baerveldt, export manager for the Washington Apple Commission, Wenatchee. “But certainly any kind of a unilateral tariff activity that restricts trade is concerning to us.”

Although the Fresh Produce Association of the Americas, Nogales, Ariz., deals with products imported into the U.S. from Mexico and not vice versa, the organization is watching this issue very closely.

“Now that Mexico has (announced intentions to retaliate), we’re worried about further retaliation from the U.S.,” said Allison Moore, FPAA communications director. “The U.S. is in direct violation of the NAFTA agreement, and Mexican officials feel many in the U.S. have couched this as a safety issue.”

Highway safety is the biggest issue for most opposed to the trucking program, which includes the Teamsters Union.

According to media reports, Obama administration officials have responded to Mexico’s threat by promising to implement a different trucking program that works for both countries.