From the NRA:

The article states that ICE had hatched a plan to use license plate readers (LPRs) at Southern California gun shows to compare information on vehicles parked at the shows with information on vehicles later crossing the border into Mexico.

Of course, there’s nothing inherently suspicious about attending a gun show or traveling to a neighboring country, even if one event precedes another. 

“Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the Government for a redress of grievances.”

“The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no Warrants shall issue, but upon probable cause, supported by Oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized.”