UPDATE (9:30 a.m. EDT): One of the "Shut Down All Ports of Entry" organizers has shed more light on why the protest was called off hours before it was supposed to begin: cartel threats.
"It was [a] cartel threatening a blood bath, [Facebook] hits coming [en] masse from Mexico," Stasyi Barth told TheBlaze Saturday. "One of the organizers was being followed and was verbally told not to go."
The plan had been to take a stand for American sovereignty, with ordinary citizens taking action to block the ports of entry along the U.S. border.
But early Saturday morning, a lead organizer of the "Shut Down All Ports of Entry" protest pulled the plug: Because of "an unsubstantiated threat of mass violence to attendees," the event was cancelled mere hours before it was supposed to begin.
SAN DIEGO, CA - NOVEMBER 14: Seen from a U.S. Customs and Border Protection helicopter, traffic passes between Mexico and the United States at the San Ysidro port of entry on November 14, 2013 near San Diego, California. San Ysidro is the busiest port of entry into the United States, with some 90,000 people crossing the border daily. John Moore/Getty Images
Citing the threat of violence and "suspicious activity" on the group's Facebook page, Stasyi Barth said the protest was cancelled around 5 a.m. EDT Saturday.
"Your lives, and the lives of our law enforcement, are more important than any protest," she wrote.
The protest had called for "deeply concerned" Americans to coordinate en masse and drive up to ports of entry all along the U.S. border and stop their vehicles, with the hope, organizers said, that the resulting economic disruption would force elected officials on both sides of the border to find solutions to illegal immigration into the U.S.
"[Support for the protest is in] Arizona, Texas, everywhere," Barth, who's based in California, told TheBlaze on Friday. "We have a Constitution that's not being abided by. Americans are losing their rights, and America is losing its sovereignty."
On Friday, Barth said she could not say how many people planned to participate in the protest, though the number of members of the "Shut Down All Ports of Entry" Facebook group — nearly 2,000 early Saturday — gives some indication.
The planned protest had been painted as a militia movement and criticized by government officials and law enforcement over the past few weeks, but Barth stressed that the protest was always meant to be a peaceful affair.
Here's the list of ports of entry that had been slated for closure, as Breitbart reported:
Texas: Laredo, Rio Grande City, Presidio, Hildago, Brownsville and Del Rio.
California: Calexico West, Calexico East, Stay Mesa, Tecate and San Ysidro.
New Mexico: Columbus and Santa Theresa.
Arizona: Naco, Nogales, Douglas and San Luis.
It remains unclear whether protestors might still show up despite the cancellation for the protests, which were slated to begin at 11 a.m. EDT Saturday.
It was also unclear early Saturday how law enforcement, which had prepared to deploy "whatever force is necessary" to keep the ports open during the protest, might investigate the threats of violence that got the event cancelled.
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