PORTLAND, Maine (AP) The American Civil Liberties Union affiliates of Maine, New Hampshire and Vermont are asking a bus company to refuse access to immigration agents who want to board and conduct citizenship checks.

The Portland Press Herald reports the affiliates sent a letter to New-Hampshire based Concord Coach Lines Tuesday asking it to reconsider its position.

The letter cites U.S. Customs and Border Protection training documents as evidence that the company has a choice of whether to allow immigration officers to board buses.

The company said it won’t put staff in the position of determining whether an agent’s burden of proof has been met.

The ACLU responded saying the company should consider how much harder it is for passengers to refuse consent when face-to-face with an officer.