More than 70 checkpoints the U.S. Border Patrol maintains, between 25 and 75 miles north of the border between the United States and Mexico, effectively limits the movements of thousands of undocumented immigrants in the Rio Grande Valley to a small area of southern Texas.

Some 130,000 undocumented migrants live in two of the Rio Grande Valley's four counties. Many never risk venturing out of the area delineated by the checkpoints out of fear of being apprehended by authorities and deported from the United States, The New York Times reported, based on data from the Migration Policy Institute in Washington.

"It's pretty common along the whole border area," Vicki Gaubeca, the director of the American Civil Liberties Union of New Mexico Regional Center for Border Rights in Las Cruces, told the newspaper about the situation.

The self-imposed restrictions sometimes lead to dire consequences for immigrant families, as in the case of a family whose child died while en route unaccompanied to Corpus Christi, Texas. The child's parents feared that they might be taken into custody if they tried to cross a Border Patrol checkpoint, according to Marsha Griffin, a pediatrician in Brownsville, Texas.

The checkpoints, which were ruled constitutional by the Supreme Court in 1976, have long been controversial, not only with immigration rights activists, but also with libertarians, who insist they violate Fourth Amendment guarantees against unreasonable searches and seizures.

Earlier this year, a series of YouTube videos went viral, featuring residents refusing to answer Border Patrol officers' questions at the stops, City Lab noted. The checkpoints have also caught the attention of El Paso Rep. Beto O'Rourke, a Democrat, who slammed the inspection practices as "un-American."

"I came through and was pulled over into secondary (inspection), which has never happened to me before," he said. "And then my 2-year-old son was put into a holding cell while they searched my truck. I didn't have anything worth searching for."