SAN DIEGO/EL PASO, Texas (Reuters) - Trucks inched through traffic and some stores reported fewer customers in U.S.-Mexico border towns on Wednesday as staffing shortages tied to a surge in asylum seekers slowed checkpoints and threats of the border closing scared away shoppers.

Drivers and commuters wait in line to cross to El Paso, Texas, on the international border crossing bridge Paso del Norte, in Ciudad Juarez, Mexico April 3, 2019. REUTERS/Jose Luis Gonzalez

U.S. President Donald Trump reiterated his threat to close the border, or parts of it, saying Congress could avert such a shutdown by changing laws to fix what he called immigration “loopholes.”

Business leaders on both sides of the border have lashed out against the threat, saying a shutdown would hurt supply chains and $1.7 billion in daily trade at some of the world’s busiest land crossings.

“Words have meaning, especially when they come from the White House. The mere threat of a border closure does create uncertainty, and uncertainty is the enemy of jobs, economic development and commerce,” said Jon Barela, who runs Borderplex Alliance, a U.S.-Mexico trade and economic development group.

Already, Washington’s decision to move some 750 border agents from commercial to immigration duties has triggered long delays for legitimate cross-border traffic.

Petra Gomez, 63, who owns the discount store Buy 4 Less near the Otay Mesa crossing in California, opposite Tijuana, said Trump’s threats were taking a toll.

“Many people are not crossing for fear that if they close the border, they will be trapped,” she said, referring to the tens of thousands of people who cross every day from the Tijuana area into California. “If they close the border, I will have to close because I will not have clients.”

In El Paso, Texas, small business owners also spoke of a sharp drop in sales.

“We’ve seen our customers go down by about 30 percent. I also have some co-workers who live in Juarez and say they have to get into the pedestrian lane an hour and a half before their shift starts just to cross the border,” said David Canales, supervisor at UTEA Duty Free, at the base of El Paso’s downtown international bridge, which connects the Texas city with Mexico’s Ciudad Juarez.

However, Mexican President Andres Manuel Lopez Obrador said on Wednesday there were no “serious problems” at the border, and that the government was in constant communication with U.S. authorities to keep it open.

“It’s not in anyone’s interest to close the border,” he told reporters at his regular morning news conference.

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“THE NEW GREEN GOLD”

U.S. Customs and Border Protection (CBP) has estimated that some 100,000 migrants were apprehended or encountered at the border in March, the highest level in a decade. Most are Central American families seeking asylum.

Trump has made stemming the flow of migrants across the southern border a centerpiece of his administration, likening the situation to a crisis and using that argument to justify his demand to build a wall along the frontier.

“This is one of, if not the biggest crisis this country has faced in a decade, truly, the security aspects of this, the humanitarian aspects of this have got to be addressed,” the U.S. Department of Homeland Security secretary, Kirstjen Nielsen, told Fox News in an interview on Tuesday.

But critics of Trump’s immigration policy, like Ruben Garcia, executive director of El Paso migrant shelter Annunciation House, said he saw “a lot of truth” to criticism that CBP recently held migrants in a detention enclosure under a city bridge to create a sense of chaos for media.

The CBP said it would suspend cargo operations every Saturday at one of its El Paso crossing points until it had enough staff to operate fully.

On Wednesday, some, but not all, lanes were open to commercial traffic at El Paso and Laredo, Texas, and Otay Mesa in California. The longest wait stretched up to seven hours at a section of the El Paso crossing where only one of six lanes was open at a major bridge, according to the CBP. In Ciudad Juarez, lines of trucks were longer than usual, according to a Reuters witness.

Mexico is the United States' third-largest trading partner and its largest supplier for agricultural products, including vegetables and avocados. (See graphic on trade and migration at the U.S.-Mexico border here.)

“Avocados in particular have the potential to become the new green gold in terms of prices” if a shutdown caused shortages, Moody’s said in a report on Wednesday.

Americans would run out of avocados in three weeks if imports from Mexico were stopped, Steve Barnard, president and chief executive of Mission Produce, the largest distributor and grower of avocados in the world, said this week.

The Business Roundtable, a powerful private sector lobby, said in a letter to White House officials on Wednesday that shutting the border would severely damage U.S. businesses, particularly those that depend on employees who commute daily to work from Mexico.

Luis Ventura, 23, crosses from Tijuana every day to work at a customs agency in San Diego. More than just concern over his job, he fears a shutdown would take him away from his son.

“If you close the border, either I stay in Tijuana without work or I stay here without family,” he said.