The American Civil Liberties Union of Maine and affiliates in two other states are asking Concord Coach Lines to refuse to consent to warrant-less searches by immigration agents on its buses, a move the company says it’s unwilling to make.

The request, made in a letter sent to the New Hampshire-based company Tuesday, cites newly released training documents from U.S. Customs and Border Protection that the ACLU has pointed to as evidence transportation checks are almost always consensual and passengers have the right to refuse to cooperate.

“It is clearer than ever that Concord Coach Lines has a choice to continue to allow immigration agents to board buses and search,” reads the letter that also is signed by ACLU affiliates in Vermont and New Hampshire. “Choosing to consent to these bus raids jeopardizes (Concord’s) paying passengers’ Fourth Amendment rights.”

The request from the ACLU follows months of back and forth with Border Protection and Concord on the issue, including the group’s lawsuit against Border Protection and the U.S. Department of Homeland Security for access to federal records on citizenship checks.

The ACLU said that Concord had previously indicated it would continue to allow immigration officials to board its buses based on its understanding of U.S. Department of Homeland Security guidance.

In a statement Tuesday, the company said it remains unwilling to deny federal law enforcement agents access to their buses or put staff in the position of determining whether a federal agent’s burden of proof has been met.

“While we have had little opportunity to review the information that the ACLU provided today, we have continued to follow and assess the legal issues surrounding CBP and their presence at bus stations,” the statement said. “We have put up posters at all of our stations that inform our passengers of their individual rights, and added a section to our website that provides information about the law, our customers’ rights, and links to additional resources – based partially on materials from the ACLU.”

The ACLU of Maine responded to Concord’s statement by asking the company to put itself in the place of its passengers.

“We understand that it is difficult to say no to federal law enforcement agents when they request consent to a search, just as it is always hard to resist those in positions of power,” ACLU of Maine staff attorney Emma Bond said in an email Tuesday night. “But consider how much harder it is for individual passengers to refuse consent when face-to-face with an armed officer blocking the aisle on a cramped bus. We ask Concord Coach Lines to stop putting its passengers in that position.”

Immigration inspections at transportation hubs are not a new practice.

U.S. Border Patrol, which is part of Customs and Border Protection, has the authority to conduct citizenship checks without a warrant within 100 miles of the nation’s land and coastal borders. That includes the entire state of Maine.

However, the ACLU and immigration advocates have said immigration inspections are becoming more common under new enforcement priorities from the Trump administration.

In January 2018, passengers boarding a Concord Coach bus at the Bangor Transportation Center were met by U.S. Customs and Border Protection agents asking about their citizenship. No one on the bus was arrested but at least one passenger expressed concerns that prompted the ACLU to look into immigration checks and urge companies like Concord and others to deny agents the ability to board and search their buses.

In March 2018, the ACLU of Maine joined nine other states in making a similar request of Greyhound Lines. The effort to get Greyhound to change its practices is still ongoing, ACLU of Maine spokeswoman Rachel Healy said Tuesday.

The number of immigration inspections and citizenship checks that took place in Maine this year, including the number at transportation hubs, was not immediately available from Border Protection.

“For decades, U.S. Border Patrol agents have routinely engaged in enforcement operations at transportation hubs throughout the nation,” said Michael McCarthy, a U.S. Customs and Border Protection spokesman for New England.

“Enforcement actions away from the border are within the jurisdiction of the U.S. Border Patrol and performed in direct support of immediate border enforcement efforts and as a means of preventing smuggling and criminal organizations from exploiting existing transportation hubs to travel to the interior of the United States.”