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WASHINGTON — A major Republican donor and businessman asked President Donald Trump in a letter Monday to reconsider his decision to impose costly tariffs on steel and aluminum imports.

"While I am a strong supporter of your administration's pro-growth policies and energy dominance agenda, imposing broad tariffs on steel risks unintended consequences that could jeopardize America's resurgent oil and natural gas industry," Dan Eberhart, CEO of Canary, an oilfield services company, wrote in the letter, which was obtained by NBC News.

Eberhart, who pumped $70,000 into the Republican National Committee's coffers during the 2016 election cycle and is raising money for GOP Senate candidates now, joins a growing list of longtime Trump allies trying to influence the president before he signs off on the tariffs of 25 percent on steel and 10 percent on aluminum.

Eberhart explained his concerns.

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"At Canary, we use as much domestically produced raw materials as possible, but in many cases, there's not enough high-grade steel in the United States to meet demand," he wrote to Trump. "We spend more than $10 million a year directly or indirectly on imported steel; tariffs will ad $2.5 million to our costs and result in us purchasing more finished products from abroad and doing less of (our) manufacturing at our U.S. facilities."

In addition, in an unusual rebuke of the president, House Speaker Paul Ryan's press office circulated a CNBC article Monday that tied a morning dip in the Dow Jones Industrial Average to Trump's announcement last week of the new tariffs (the Dow regained its losses and moved into positive territory in the hours after the article was published).

"We are extremely worried about the consequences of a trade war and are urging the White House to not advance with this plan,” said Ryan's press secretary, AshLee Strong. "The new tax reform law has boosted the economy, and we certainly don't want to jeopardize those gains."

And the Club for Growth, an organization with close ties to the billionaire Koch brothers, slammed Trump's plan as both a philosophical and an economic failure.

"The idea of imposing steel or aluminum tariffs of any kind is an affront to economic freedom,” Club for Growth President David McIntosh said. "We urge the Trump administration not to impose tariffs that could threaten to undo the historical economic growth the tax cuts and the president's deregulatory agenda have unleashed."

Last week, the Heritage Foundation, a leading conservative think-tank that has largely been supportive of Trump's agenda, criticized the move, too.

"Restricting imports under the guise of national security will increase prices of these basic commodities for numerous U.S. manufacturers and consumers, and put millions of American jobs at risk," Tori Whiting, a Heritage research associate, wrote. "It is not in the interest of the U.S. economy, or the 'forgotten men and women' of America, to restrict these vital imports."

Commerce Secretary Wilbur Ross, one of the plan's biggest supporters inside the administration, defended it Sunday on NBC's "Meet the Press" and said he doesn't expect the criticism to change the president's mind.

"The president has announced that this will happen this week," Ross said. "I have no reason to think otherwise."

The pushback from various sectors — a big GOP donor, the House speaker, Club for Growth and Heritage — reflects a deep antipathy toward the tariffs and the possibility of an ensuing trade war within the ranks of Republican traditionalists.