Corey El was on an Amtrak train from Penn Station to Niagara Falls last Thursday when he says a Border Patrol officer approached his seat.

“He asked me, ‘Are you an American citizen?’” he said. “I scoffed at him and said, ‘Yeah.’”

El quickly got out his phone and took a video of U.S. Customs and Border Protection officers questioning another Amtrak customer, which has since gone viral, receiving over 6,800 retweets.

The train was stopped in Syracuse, about 160 miles away from El’s destination, for about 20 minutes, he said. El remembers the officers asking two other riders for their citizenship status, and none of them were white. One passenger, who he said was “possibly Middle Eastern,” produced a burgundy passport during questioning.

“I originally wanted to tell him off and to refuse to answer. I know it’s legal,” said El. “But I’m cognizant of the fact that I’m also black. As a person of color, there’s a foot on my neck. I know that I can’t.”

The viral encounter raises a pivotal civil rights question that Amtrak wouldn’t clarify in several interactions with The Daily Beast.

Are Amtrak customers now required to bring with them proof of American citizenship, or else face being ejected from a train hundreds of miles away from their destination?

“The reason this thing goes viral is because it is outrageous,” said Jordan Wells, a staff attorney at the New York Civil Liberties Union, a branch of the ACLU. “We should be outraged at this seeming attempt to turn everyday transportation into a police dragnet where you have to respond to, ‘Papers, please.’”

The Daily Beast reached out to Amtrak, asking if passengers must prove their citizenship to remain on trains, how frequently these interrogations are taking place, and how often trains are delayed due to citizenship checks.

“Amtrak cooperates fully with federal authorities and federal law,” said company spokesperson Jason Abrams. “Amtrak customers 18 years of age and older must carry valid photo identification.”

Valid photo identification does not necessarily prove U.S. citizenship. Tourists and documented immigrants on visas are also legally allowed on Amtrak trains.

The Daily Beast once again asked if passengers who could not immediately prove citizenship, even if in they are in the country legally, could be ejected from trains for further questioning mid-journey.

Amtrak initially responded by saying, “I suggest you check with CBP for more info,” but another spokesperson later said Amtrak riders do not need proof of citizenship to ride on its trains.

“ Amtrak does not require proof of citizenship to travel on our trains,” said Amtrak media relations representative Kimberly Woods. “Amtrak cannot speak on behalf of Customs and Border Patrol or other law enforcement agencies.”

When asked again to clarify if a rider could be ejected from a train for further questioning if he or she doesn’t produce citizenship papers, Amtrak did not respond to a request for comment.

When asked for comment, a CBP spokesperson pointed to the Immigration and Nationality Act, under which Border Patrol officers can “within a reasonable distance from any external boundary of the United States… board and search for aliens in any vessel within the territorial waters of the United States and any railcar, aircraft, conveyance, or vehicle” within 100 miles of a border without a warrant.

“U.S. Border Patrol agents routinely engage in enforcement operations at transportation hubs throughout New York and Pennsylvania,” the spokesperson said.

“Although most Border Patrol work is conducted in the immediate border area, agents have broad law enforcement authorities, including the authority to question individuals, make arrests, and take and consider evidence.”

Syracuse’s Amtrak station is within 100 miles of the Canadian border by air.

Wells said this interpretation of the law is “not carte blanche authorization to violate people’s civil rights.”

“ You have a right to deny any request to search your belongings. Even if you’re undocumented, you have the right to decline. ”

“Maybe it’s because we go through a port of entry like an airport, we submit to searches. But this 100-mile zone is much different than at a point of entry. It covers two-thirds of the population of the U.S,” said Wells. “It could not possibly be that that would be a zone where the Constitution is not enforced.”

Wells said Border Patrol officers asking for proof of citizenship can create “a Fourth Amendment problem, if people don’t feel they can terminate the encounter and walk away.”

“You have a right to deny any request to search your belongings. Even if you’re undocumented, you have the right to decline [showing citizenship papers]. You have the right to remain silent, and that silence should not be used to forcibly detain somebody,” said Wells.

Wells said situations like El’s could also pose “an equal protection problem under the Constitution” if the demands for proof of citizenship were selectively based on race or ethnicity.

CBP’s spokesperson said carrying documentation is not “required.”

“U.S. citizens are not required to carry any documentation that would prove their citizenship. With that being said, the best way to prove citizenship is with a passport, their birth certificate, or with an enhanced driver’s license from states that have them,” the CBP spokesperson said. “Aliens, on the other hand, are required by law to carry documentation proving their right to be or remain in the United States. False claims to U.S. citizenship are in violation of immigration law.”

CBP did not respond when asked if a rider could be ejected from a train for further questioning if he or she didn’t produce papers.

While Wells said train and bus searches are “not a Trump-era phenomenon exclusively,” the searches do appear to be happening more frequently since Donald Trump became president.

“The aggressive enforcement without regard to constitutional limits is playing out not just in Customs and Border Protection but the Department of Homeland Security in general,” Wells said.

El said the 20-minute immigration document stoppage on his Amtrak train “set us back schedule-wise.” But he was much more concerned about the potential civil rights implications of the interaction.

“Who carries around a birth certificate?” he asked. “This is some slavery shit, like ‘Show me your freedom papers.’”