Congressional Republicans are leveling some rare and uncharacteristically harsh criticism of President Trump for his decision to increase imports of ground beef at a lower tariff rate, warning that the move will hurt American ranchers.

The decision, announced late last week, appeared to be a bid to lower costs across the country before the midterm elections in which Republicans are fighting to preserve their narrow majorities. But it has drawn dissent from even reliable allies of Mr. Trump, many of them from states and districts with large cattle-raising areas, who fear that the move could harm another important constituency: the producers they represent.

“Americans want U.S. beef on the table — not foreign imports,” Senator John Barrasso of Wyoming, the No. 2 Republican, said in a statement on Monday. “Wyoming ranchers produce the highest-quality beef in the world. Our ranchers don’t ask for special treatment. They simply want a fair marketplace.”

Senator Tim Sheehy, Republican of Montana, said in a lengthy statement that he had “advised President Trump against this course of action for a year because American ranchers have been struggling against the packer monopoly for decades, and this will further harm them.”

“Most of whom are MAGA Republicans,” he added.

The cascade of statements — including from Senators Pete Ricketts of Nebraska, Steve Daines of Montana and Cindy Hyde-Smith of Mississippi — amounted to an unusual chorus of protest from Republicans who have otherwise routinely deferred to Mr. Trump on nearly every major issue, from the war with Iran to his trade wars.

Most Republicans have repeatedly voted against efforts to cancel Mr. Trump’s tariffs or rein in his power to continue the conflict with Iran, even as both have driven up prices ahead of the November elections.

Their public expressions of unhappiness were all the more notable given that they came during a summer recess, when lawmakers are away from Washington and the Capitol press corps. Members of both parties typically take advantage of such absences to avoid commenting on politically tricky developments.

In this case, several Republicans said that they had contacted senior Trump administration officials in an attempt to persuade Mr. Trump to reverse course.

“I have reached out to the one person I’m convinced that the president listens to and respects the most on this subject to highlight concerns and suggest a focus on that which could serve both consumers and cattle producers jointly,” Representative Josh Brecheen of Oklahoma said, without elaborating.

The issue has been a long-simmering one among Western Republicans. Last fall, after the White House announced it would quadruple the amount of Argentine beef it allows into the country annually at a lower tariff rate, Republican senators pressed Vice President JD Vance to abandon the plan at an unexpectedly heated private luncheon.

At the time, Republican lawmakers said they had received hundreds of calls from upset ranchers in their states, and many of them had privately registered their unhappiness with the White House.

“Let’s just say: Message received,” Mr. Daines said after the luncheon.

But over the weekend, Republicans heard another earful from upset ranchers. The National Cattlemen’s Beef Association said the administration’s “repeated whiplash on trade policy and beef imports has real impacts.”

The White House announcement, the group said in a statement, was “not about putting their finger on the scale for one cattle industry group or another. It is 100 percent about the 74 days between now and the midterm elections.”