WASHINGTON — U.S. agriculture groups said new tariffs on steel and aluminum from Mexico, Canada and the E.U. will hurt relationships with those key trading partners and likely result in counter measures against agriculture products.

“Based on information we have heard from our customers and past experience, we have every reason to believe U.S. agriculture, including the products we represent, will be among the first hit by counter measures from our trading partners,” said Tom Sleight, president and chief executive officer of the U.S. Grains Council. “We had strong hopes this situation would be averted permanently, but it now appears we need to prepare for retaliation and its direct impact U.S. farmers. Our global staff is doing this to the best of their abilities as we continue to follow new developments.”

U.S. President Donald Trump announced in March tariffs on steel and aluminum from selected countries, but gave temporary exemptions to Mexico, Canada and the E.U. as negotiations over limits were ongoing. The exemptions expired on June 1.

Mr. Trump said the administration will continue discussions with the nations and remains open to discussions with other countries.

The U.S.G.C. said the latest nations subjected to tariffs are among the U.S.’s closest neighbors and friends.

“We have spent years building markets in these countries based on a mutual belief that increasing trade benefits all parties,” Mr. Sleight said.

In response, Canada said it intends to impose surtaxes or similar countermeasures up to C$16.6 billion on imports of steel, aluminum and other products, including yogurt, certain prepared foods and coffee. The government is considering whether additional measures are needed.

Mexico also said it will impose equivalent measures on various products, including flat steel, lamps, pork legs and shoulders, sausages and food preparations, some fresh fruits and various cheeses.

Jean-Claude Juncker, president of the European Commission, said the U.S. tariffs are unjustified and at odds with World Trade Organization (W.T.O.) rules.

“The U.S. now leaves us with no choice but to proceed with a W.T.O. dispute settlement case and with the imposition of additional duties on a number of imports from the U.S.,” Mr. Juncker said.

Kevin Skunes, president of the National Corn Growers Association’s (N.C.G.A.), said the uncertainty brought on by the tariffs comes at a time when net farm income has dropped 52%.

“This uncertainty impacts every step of the agriculture economy, from securing financing to marketing,” he said. “Imposing tariffs has the potential to undermine positive relationships with our closest allies and erode long-standing market access. N.C.G.A. urges policymakers to strengthen cooperation with our trading partners and stay at the negotiating table.”