Concord — A Concord Coach employee “was caught off guard” by the arrival of a customs official and “made a mistake” when he told people boarding one of the company’s buses in Maine that they had to be U.S. citizens to ride, the Concord-based company said in a statement prompted by a video of the incident.

“We support our passengers’ right to decline to answer questions from CBP,” the statement said, referring to U.S. Customs and Border Protection.

The statement came in response to a video posted by a person boarding a Concord Coach bus in Bangor, Maine, showing a U.S. Border Patrol agent asking each person in line on Memorial Day whether they are a U.S. citizen, a question that at least one rider refused to answer.

When a prospective rider asks a Concord Coach employee, “Do you have to be a U.S. citizen to take this bus?” the employee answers yes, twice, to which the rider responds, “I doubt that.”

The video drew sharp criticism from the New Hampshire chapter of the ACLU.

“People should be able to take the bus without fear of unfounded interrogation and deportation. Concord Coach has the right to say no to border patrol,” said Gilles Bissonnette, the chapter’s legal director.

Concord Coach Lines Vice President Ben Blunt said over the weekend that the employee was mistaken in telling riders they had to be citizens, a position the company reiterated in its statement on Sunday.

Concord Coach provides intercity bus service throughout Maine and New Hampshire, and into Massachusetts. The bulk of its business is in Maine.

Concord Coach Lines also operates Dartmouth Coach.

“The vast majority of the time that (U.S. Customs and Border Protection, or CBP) is present at our facilities, they arrive without any forewarning and we have very limited interaction with them,” the statement said. “Like any transportation company, this is true of all law enforcement agencies. … The CBP typically questions passengers in common areas like the boarding and loading docks that are open to all customers.”

As for the video, the statement claimed, “The terminal employee was caught off-guard with a question that he was unprepared to answer and made a mistake that we share.”

Border Patrol agents have more extensive authority to question people within 100 miles of an international border.

This region includes all of Maine and virtually all of New Hampshire, even areas that are further than 100 miles from the land border with Canada, because the coastline is also considered an international border.

Bangor is the northern-most major city in Maine, located slightly farther north than Berlin.