SYRACUSE, N.Y. -- Are you an American Citizen?

That's what a border patrol agent asked Corey El, 27, of Brooklyn as he traveled to his parents' home in Niagara Falls on an Amtrak train that was stopped Thursday in Syracuse.

"I was shocked," El said. "I just said 'yeah.'"

The border patrol officer moved on, bypassing some people and asking other people the same question: Are you an American citizen?

The checks were captured on a video by El which he posted on Twitter Thursday afternoon. By Friday the video had more than 625,000 views, 5,100 likes and 1,300 comments.

These types of checks by border patrol agents, which experts say are legal under federal law, are happening more often and are sometimes captured by passengers on their cell phones.

Last month a similar encounter with Florida border patrol agents on a Greyhound bus gained national attention after a woman was detained in Fort Lauderdale. The woman had an expired tourist visa and was arrested, according to the Miami Herald.

"There are several videos just like this on Twitter," said Syracuse University Associate Professor Elizabeth Cohen, who teaches political science at the Maxwell School of Citizenship and Public Affairs.

Cohen said the Fourth Amendment of the U.S. Constitution protects Americans from random and arbitrary searches and stops, but those right do not apply at the borders.

Under federal regulations, Syracuse is considered a border area. U.S. Customs and Border Protection have authority within 100 miles of any U.S. border, Cohen said. Syracuse is 97 miles from the Canadian border near Alexandria Bay.

In this 100-mile zone, border patrol agents need "reasonable suspicion" of an immigration violation or crime to stop or search a person, according to the American Civil Liberties Union. Outside the zone agents need warrants and probable cause to stop people and question them, Cohen said.

Do you have to answer border patrol agents' questions?

"People are often advised to refuse to speak to a Custom and Border Protection agent," Cohen said. "But once a search is under way, that may not be helpful."

"Keeping silent if one believes one may need legal representation is often recommended by lawyers," Cohen said. "But, on its own, simply refusing a request for documentation will not end an investigation and people are often taken into custody if they are suspected of not having proper documentation."

Cohen said agents are often looking for expired visas, such as the case in Florida, or those who are undocumented.

El said he felt that the agent's questioning was wrong and represented racial profiling. He said the officer moved on after talking to him, bypassing white passengers, and asking other people of color the same question about whether they are American citizens.

He watched as the agent questioned passengers. He said he saw one person hand over a passport.

The incident left El upset and frustrated. He said he never saw this happen in real life but noted that he watched Florida's viral Greyhound video last month.

"It was shocking and I absolutely felt like I was profiled," El said due to his race/ethnicity -- he's black and Latino -- and his last name that he said is his father's Islamic name. "It makes me angry."

Amtrak said in a statement to Syracuse.com that the company cooperates fully with federal authorities and federal law. Amtrak customers 18 years of age and older must carry valid photo identification, according to the statement.

At the end of El's video you can hear an agent ask a person if they are an American citizen.