Sealing the border with Mexico, America’s third-largest trading partner, would disrupt supply chains for major U.S. automakers, trigger swift price increases for grocery shoppers and invite lawsuits against the federal government, according to trade specialists and business executives.

“First, you’d see prices rise in­cred­ibly fast. Then . . . we would see layoffs within a day or two,” said Lance Jungmeyer, president of the Fresh Produce Association of the Americas in Nogales, Ariz. “This is not going to help border security.”

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Two of the president’s most senior aides nonetheless defended the move on the Sunday news shows. Acting White House chief of staff Mick Mulvaney said on ABC News’s “This Week” that it would take “something dramatic” to persuade the president to abandon his border-closing plans. And Counselor to the President Kellyanne Conway insisted on “Fox News Sunday” that the president’s threat “certainly isn’t a bluff.”

Trump sparked the latest immigration-related controversy Friday when he complained to reporters about Mexico’s failure to stem the migrant influx, a point he underscored in a tweet the next day. “If they don’t stop them, we are closing the border. We’ll close it. And we’ll keep it closed for a long time. I’m not playing games,” Trump said Friday.

Administration officials have offered no details about the president’s intentions, and border control officials have received no instructions to prepare for a shutdown, according to a U.S. Customs and Border Protection official, who spoke on the condition of anonymity to discuss the issue. Implementing such an order would require time to notify Congress and labor unions representing Border Patrol agents and customs officers, the official said.

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A Pentagon spokesman said the military, which has about 5,300 troops in the border region, has not received such orders either.

Mexican officials have tried to avoid inflaming the situation, offering no public comment since Friday, when President Andrés Manuel López Obrador said: “We are going to help, to collaborate. We want to have a good relationship with the government of the United States. We are not going to argue about these issues.”

Closing the border could complicate efforts to secure congressional ratification of Trump’s new trade deal with Mexico and Canada, said economist Phil Levy, who worked on trade issues in the White House under President George W. Bush and is now a senior fellow at the Chicago Council on Global Affairs.

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The U.S.-Mexico-Canada Agreement, the signature achievement thus far of the president’s “America First” trade offensive, faces an uphill battle in Congress.

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The U.S.-Mexico border is a key artery in the global economy, with more than $611 billion in cross-border trade last year, according to the Commerce Department. Each day, more than 1,000 trucks cross the border at the port of Calexico East, Calif., while more than 11 daily international trains go through Laredo, Tex., according to the U.S. Transportation Department.

In Laredo, business leaders and elected officials held frantic conference calls over the weekend about the threatened closure. Gerry Schwebel, executive vice president of the international division of Laredo-based IBC Bank, said U.S.-Mexico traffic has occasionally been restricted, but only temporarily and only in the event of emergencies, such as floods, tornadoes or security checks after the Sept. 11, 2001, terrorist attacks.

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Even a border slowdown could create shortages of goods and services and lead to higher prices for consumers, he said, adding: “If you want to create an economic crisis, then shutting down the border will create an economic crisis.”

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The economic consequences of a complete shutdown would be immediate and severe, trade specialists said, with automakers and American farmers among the first to feel the pain.

“It’s unworkable and unrealistic, and I don’t think he could really do it,” said Rufus Yerxa, president of the National Foreign Trade Council, which represents multinational corporations. “There would certainly be legal challenges from lots and lots of companies.”

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In his TV appearances, Mulvaney also reiterated the administration’s intention to end hundreds of millions of dollars in assistance to the “Northern Triangle” countries of Guatemala, Honduras and El Salvador, including programs designed to curb the gang violence that has caused many people to flee north.

The three nations are the primary source of a growing wave of migrants, including caravans of families with children, who have been crossing the U.S. border to seek asylum in an escalating humanitarian crisis.

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“Democrats didn’t believe us a month ago, two months ago when we said what was happening at the border was a crisis, a humanitarian crisis, a security crisis,” Mulvaney said on “This Week.”

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He called on the Mexican government to tighten its southern border and said Guatemala, Honduras and El Salvador need to do more to prevent their citizens from entering Mexico.

Until they do, Mulvaney said, the administration sees a need to close ports of entry to free up border agents “to go out and patrol in the desert, where we don’t have any wall.”

That redeployment of border agents threatens to pinch commerce. On Friday, the Border Patrol’s Tucson field office issued a notice that it would immediately end Sunday processing of commercial trucks at the Port of Nogales, Ariz.

To deal with “an unprecedented humanitarian and border security crisis all along our Southwest border,” the agency said it had redeployed 750 border agents from ports of entry to areas affected by the migrant flood.

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Jungmeyer, the produce industry representative, said the reduction to six days of operation each week will have a significant effect on the fresh produce industry, which operates on a “just-in-time” schedule of deliveries.

At this time of year, trucks travel to Mexico to collect watermelons and table grapes. Once full, they head for the United States, where they drop their cargo at American warehouses before quickly returning to Mexico for another load.

Eliminating one workday at a port that handled 337,179 trucks last year would disrupt that carefully-calibrated schedule.

“It messes up harvests. It messes up your ability to service customers on the U.S. side of the border,” Jungmeyer said.

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Suddenly halting the passage of people and goods between the United States and Mexico also would interrupt the flow of parts headed to American factories, which could bring some production to a halt. Likewise, refrigerated trucks full of perishable commodities such as beef would jam border crossings.

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“The first question would be: Where do you put it?” said William Reinsch, who served in the Commerce Department under President Bill Clinton. “Stuff is going to stack up at the border because it’s already on the way there.”

Arturo Sarukhan, Mexico’s ambassador to the United States from 2007 to 2013, said farm states, many of which backed Trump in 2016, would be among the casualties. Closing the border would be a “self-inflicted wound,” he said.

“I’m not going to try to second guess whether the president is playing chicken, bluffing or spewing whatever comes to his mind,” Sarukhan said Sunday. “The reality is that it would be extremely costly for the United States in terms of trade and economic well being.”

Stephen Legomsky, professor emeritus at the Washington University School of Law and former chief counsel of U.S. Citizenship and Immigration Services, said closing the ports would likely end up in court because it would violate federal immigration laws.

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Trump “cannot close every port on the border,” Legomsky said. “If he did so, he would effectively undermine the entire congressional scheme for who may enter the U.S. and who may not.”

Closing the border is also unlikely to stanch the influx of asylum seekers, he said, because federal law authorizes them to request protection once they step on U.S. soil. “If anything, closing the authorized points would just drive more traffic between the ports of entry where people can enter illegally,” he said.

Administration officials insist that inaction is not an option. About 100,000 migrants are believed to have arrived at the border this month, Mulvaney said, a human tide that has overwhelmed U.S. authorities and sparked profound partisan disagreement over potential remedies.

On Saturday, Trump tweeted: “Our detention areas are maxed out & we will take no more illegals. Next step is to close the Border!”