SEATTLE (AP) — A Customs and Border Protection memo obtained by The Associated Press confirms that bus companies such as Greyhound do not have to allow Border Patrol agents on board to conduct routine checks for immigrants in the country illegally, which is contrary to the company's long insistence that it has no choice but to do so.

Greyhound, the nation's largest bus carrier, has said it does not like the agents coming on board, but it has nevertheless permitted them, claiming federal law demanded it. When provided with the memo by the AP, the company declined to say whether it would change...