A farmer fills seed boxes on a Case IH Agricultural Equipment planter while planting corn in Princeton, Illinois, April 24, 2018. Daniel Acker | Bloomberg | Getty Images

President Donald Trump's threatened 5% tariff on all Mexican imports could hit American farmers especially hard if Mexico retaliates with punitive duties on U.S. agricultural products. Farmers are already reeling from Trump's drawn out trade war with China and fear further losses could be in their futures. "When you look at all the different products that the U.S. exports to Mexico, all those folks are getting nervous that retaliatory tariffs could certainly find their way onto their products," said Veronica Nigh, an economist with the American Farm Bureau Federation, the nation's largest farm sector organization. Mexico is considered one of the most lucrative markets for American agriculture products given its easy access and close proximity to the U.S, whether via rail, ship or truck. Even so, that hasn't stopped other countries from chipping away at American agricultural dominance when it comes to supplying its neighbor to the south with grains, meats and other farm products. The U.S. exported $19 billion in agricultural exports to Mexico last year, making it the second-largest purchaser after Canada, according to the U.S. Department of Agriculture. Mexico is the top market for U.S. corn, rice, dairy products, poultry, eggs, pecans and also a major buyer of American beef, pork, soybeans and wheat.

Farmer walks through his soy fields in Harvard, Illinois. Nova Safo | AFP | Getty Images

Frustrated with Central American migration, the White House last Thursday announced the U.S. plans to slap 5% tariffs on Mexican goods, including cars, beer, tequila, as well as fruits and vegetables. The duties would start June 10 and gradually increase to 25% on Oct. 1 unless Mexico "substantially stops the illegal inflow of aliens coming through its territory." "If you put a tariff on imported goods, usually that price gets passed to consumers," said Luis Ribera, an agricultural economist at Texas A&M University. "And you can expect that Mexico will retaliate one way or another." Mexican officials in Washington this week as part of a diplomatic push to avert new tariffs are warning the levies won't stop the flow of migrants. Talks between U.S. and Mexican officials on Wednesday failed to produce a deal, a senior administration official told NBC News. Trump slapped tariffs last year on imported steel and aluminum, resulting in Mexico imposing levies on $3 billion of U.S. goods, including a variety of agricultural products. The U.S. last month lifted metals tariffs against Mexico and Canada as part of a push to get ratification of the pending United States-Mexico-Canada Agreement. However, Trump's threat to impose new tariffs against Mexico over immigration puts USMCA in jeopardy and raises the risk of additional financial fallout for American farmers already hurting from the escalating trade war with China. The new USMCA is designed to replace the North American Free Trade Agreement, a 25-year-old pact between the U.S., Canada and Mexico.

"Amid a perfect storm of challenges in farm country, we cannot afford the uncertainty this action would bring." Lynn Chrisp president, National Corn Growers Associatiop