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 that practice.

Greyhound has faced pressure from the American Civil Liberties Union, immigrant rights activists and Washington state Attorney General Bob Ferguson to stop allowing sweeps on buses within 100 miles (160 kilometers) of an international border or coastline.

They say the practice is intimidating and discriminatory and has become more common under President Donald Trump. Border Patrol arrests videotaped by other passengers have sparked criticism, and Greyhound faces a lawsuit in California alleging that it violated consumer protection laws by facilitating raids.

Some other bus companies, including Jefferson Lines, which operates in 14 states, and MTRWestern, which operates in the Pacific Northwest, have made clear that they do not consent to agents boarding buses.

The memo obtained by the AP was dated Jan. 28, addressed to all chief patrol agents and signed by then-Border Patrol Chief Carla Provost just before she retired. It confirms the legal position that Greyhound’s critics have taken: that the Constitution’s Fourth Amendment prevents agents from boarding buses and questioning passengers without a warrant or the consent of the company.

“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,” the memo states. An agent’s actions while on the bus “would not cause a reasonable person to believe that he or she is unable to terminate the encounter with the agent.”

Border Patrol officials have previously said agents do seek the consent of the bus driver before boarding and questioning passengers. Bill Kingsford, the operations officer for the Border Patrol’s Spokane, Washington, sector, said Thursday that before the memo he had never seen that policy in writing.

In response to criticism over the past two years, Greyhound has said that it does not support or “consent” to the bus searches, but that federal law left it no choice. The company said the immigration sweeps make for delays, missed buses and unhappy customers.

Greyhound’s parent company, FirstGroup PLC, said last summer: “We are required by federal law to comply with the requests of federal agents. To suggest we have lawful choice in the matter is tendentious and false.”

Greyhound said that it appreciated the Border Patrol “clarifying” its policy. “We were unaware of USBP’s memo clarifying their practices regarding transportation and bus check operations,” the company said. “We are pleased there appears to be greater context about these practices as we have publicly stated we do not consent to these searches and maintain that position.”

The statement said it would continue to request guidance from the Border Patrol. “Our goal is to ensure that our passengers and drivers feel safe and secure when riding with us, and we’ll continue to make that our top priority.”

Advocates said the memo could give them additional leverage.

“This puts the pressure on Greyhound,” said Matt Adams, legal director of the Northwest Immigrant Rights Project. “Are you going to stand up and protect your customers or are you going to collaborate with the government and turn over your passengers to the Border Patrol?”

ACLU chapters in 10 states — California, Washington, Vermont, New York, New Hampshire, Michigan, Florida, Maine, Texas and Arizona — wrote to Greyhound in 2018 to express their concern with passengers being pulled off buses and arrested. In several cases, they said, it appeared passengers had been singled out and questioned based on having dark skin or foreign accents.

The Border Patrol denies that, saying all passengers are questioned.

“Greyhound must take a firm stance — issue a public statement, add signage to buses and stations, train and empower employees, etc. — to make it abundantly clear that the company as a whole does not consent to these searches,” said Andrea Flores, deputy director of policy at the ACLU’s Equality Division.

Washington’s state’s Democratic attorney general has threatened legal action, saying that Greyhound’s acquiescence to the Border Patrol causes travel delays as well as alarm and confusion for patrons — in potential violation of state consumer protection law. He asked Greyhound last year to take several steps, including posting stickers on its buses notifying the Border Patrol that it does not consent to searches, but the company has so far declined to do so.

Other bus companies contacted by the attorney general’s office have placed stickers on their doors noting that the company does not consent to searches or have given drivers placards to hand to agents explaining the refusal.

“This memo is consistent with what my office has been saying all along to Greyhound,” Ferguson said in a statement. “Unfortunately, Greyhound continues to demonstrate indifference to the legal rights of its customers. If Greyhound refuses to recognize their legal obligations, then we will be forced to take action.”

Under then-President Barack Obama, Customs and Border Protection in late 2011 began cutting back on so-called “transportation checks,” especially along the U.S.-Canada border, amid criticism that it amounted to racial profiling. The agency told agents to keep away from bus and train stations entirely unless they had “actionable intelligence” about someone who had recently entered the country illegally. It also said such operations had to be cleared with Border Patrol headquarters in Washington, D.C.

The Trump administration returned authority to the chief agents in each Border Patrol sector to approve the operations, and they have been on the rise, the agency says.

In a statement, the CBP said that “enforcement operations” are routine at transportation hubs and “are performed consistent with law and in direct support of immediate border enforcement efforts.”

“The U.S. Border Patrol conducts regular outreach with transportation companies to foster good working relationships,” the statement said.

The agency has especially faced criticism for conducting the checks on buses far from the border. In Spokane, just under 100 miles (160 kilometers) from Canada, arrests at the city’s bus depot rose from 35 in 2017 to 84 last year, according to data obtained by the University of Washington’s Center for Human Rights. Bus routes there run east and west and don’t cross the border.

Among those detained in Spokane last year was Portland, Oregon, comedian Mohanad Elshieky, who was removed from a Greyhound bus as he returned home from a performance. Elshieky, a Libyan citizen who was granted asylum in the U.S., said he was detained for 20 minutes, even though he had two forms of identification showing that he was in the country legally.

Elshieky’s attorneys sued the government for false arrest in a federal lawsuit Friday. At the time of the detention, CBP said Elshieky should have been carrying different identification to prove his immigration status. The agency said it does not comment on pending litigation.