What is the difference between immigration checkpoints at airports and on highways?

The Associated Press

U.S. Border Patrol Senior Agent B.T. Hick and his dog Mirza, left, inspect a car at a check point outside Organ Pipe Cactus National Park in Why, Ariz., Wednesday, May 24, 2006. The detention of a prominent immigration activist at a Texas airport served as a reminder of the latitude the Border Patrol has in conducting checkpoints for drugs and immigrants in the country illegally at locations not on the border. (AP Photo/Matt York, File)

Associated Press + More

By ASTRID GALVAN, Associated Press

TUCSON, Ariz. (AP) — The arrest of a prominent immigration activist and former journalist at a Texas airport was a reminder of the authority that the U.S. Border Patrol has in conducting checkpoints.

Jose Antonio Vargas, a Pulitzer Prize winner, was detained at the McAllen/Miller International Airport in south Texas this week after being questioned about his citizenship status while visiting the region to attend vigils related to the Central American immigration surge. For many who do not live in border states, the idea of being asked for immigration status while flying within the U.S. seems foreign. Here are some details about why and how the U.S. Border Patrol operates in airports and locations along the country's border.

WHAT DO BORDER PATROL AGENTS DO AT AIRPORTS?

Border Patrol agents who work at airports within 100 miles of the border are often in plain clothes and work closely with Transportation Security Administration agents to monitor people, even those who are flying within the country. Agents don't typically have offices within the airport, and the Border Patrol will not say how many agents staff airports at any given time.

But they are there.

They check passports, green cards, and other forms of identification while standing over the shoulder of a TSA agent. Essentially, agents are on the lookout for suspicious behavior such as extreme nervousness or appearing to be lost. If an agent sees that such a person presents a green card but looks nervous, the agent would likely question that person. The agent would ask questions such as where the person's mother was born and how long it's been since they entered the country to determine whether the ID they are using is counterfeit.

In the case of Antonio Vargas, Border Patrol agents were standing alongside TSA personnel at the McAllen/Miller International Airport, which is only a few miles from the U.S.-Mexico border, when the activist tried going through. Vargas does not have a government-issued U.S. identification card, and uses a passport issued by his native Philippines. He was arrested after telling an agent that he was in the country illegally. Vargas was released Tuesday on his own recognizance with a notice to appear before an immigration judge.

DOES THE BORDER PATROL OPERATE CHECKPOINTS ON ROADS, TOO?

Yes. The border patrol has dozens of in-land checkpoints around the Southwest and in northern states such as Washington. The checkpoints can be within 100 air miles of the country's border. They are usually located on highways and small roads. For example, there is a makeshift checkpoint on a two-lane road just outside a small Arizona town called Arivaca, where residents are protesting the border patrol's presence. The town is 20 miles from the border.

Arivaca residents, regardless of their citizenship and immigration status, must pass through the checkpoint every time they leave town, which is regularly because the town does not have schools or a large grocery store and many residents work outside the town. They are asked whether they are U.S. citizens. The ACLU says the border patrol can only briefly detain travelers, and they cannot use checkpoints for "general crime control."

WHAT ARE THE MAJOR DIFFERENCES BETWEEN WHAT BORDER PATROL AGENTS DO AT ROAD CHECKPOINTS AND WHAT THEY DO AT AIRPORTS?

Checkpoints are clearly marked. All people who drive through a checkpoint are asked to reveal whether they are U.S. citizens — that is not the case at airports. And while agents at checkpoints are in full uniform, those at airports are more likely to be in plain clothes. One thing they have in common: They use the study of behaviors to determine whether someone might be without legal status or committing a crime. And both are used more as deterrents than they are for catching criminals.

DO BORDER PATROL AGENTS MONITOR AT ALL AIRPORTS?