The Fourth Amendment to the Constitution guarantees everyone protection from unreasonable searches and seizures. But the management of Concord Coach Lines has said that it is unclear whether that fundamental right applies to its customers.

So the New Hampshire-based carrier has been permitting Border Patrol agents to board its buses in order to question passengers.

We have never seen how this kind of “show me your papers” policing could be consistent with the Constitution, but any confusion on the part of the bus company should be cleared up now — and by the federal agency itself.

In a leaked document published this month by the Associated Press, we have learned that a top Border Patrol official had advised agents that they needed to get permission from a bus company before coming on board. “When transportation checks occur on a bus at non-checkpoint locations, the agent must demonstrate that he or she gained access to the bus with the consent of the company’s owner or one of the company’s employees,” then-Border Patrol Chief Carla Provost wrote Jan. 28, shortly before her retirement.

From this memo it should be clear that the bus company is not required to comply. The only reason a Border Patrol agent can stand in the aisle of a cramped bus to question random passengers in their seats is that the bus company has given them permission to be there.

Armed with this information, Greyhound, the country’s largest bus line, has announced that it will no longer permit warrantless immigration checks aboard its buses, and New Hampshire-based Concord Coach Lines has announced that it would review its policy.

That review should result in Concord following Greyhound’s lead, and protecting its customers from this form of official harassment.

Border Patrol agents have become increasingly aggressive in the last two years, patrolling much more than the border. They assert a 100-mile zone of jurisdiction measured from any international border or coastline. This puts the entire state of Maine under their purview.

The agency has claimed that this also gives them the authority to question bus passengers, even if the bus is not going anywhere near an international border.

These onboard citizenship checks are intimidating. Technically, no one is required to answer questions, but many would find it difficult to refuse when confronted in tight quarters by an armed officer. And although the agency denies any racial profiling, viral cellphone videos recorded by bus passengers have circulated showing agents who focus on people of color or who have accented speech, asking to see citizenship documents.

In addition to citing the need for the bus company’s consent, Provost’s memo also describes conditions for the interviews that are at odds with what bus passengers report seeing. These interviews must be conducted in a way, she wrote, that “would not cause a reasonable person to believe that he or she is unable to terminate the encounter with the agent.”

The bus companies have said in the past that they have no choice in the matter because federal law requires them to allow the agents on board. But the Border Patrol memo should clear up any confusion.

Concord Coach Lines is not required to subject its customers to random interrogation by the Border Patrol. The company can stop letting it happen, and it should.