As the Trump administration aggressively expands its effort to force migrants to remain in Mexico while they await U.S. immigration court hearings, lawyers for those seeking asylum are urging a federal appeals court to halt the government program.

Known as the Migrant Protection Protocols, the program has been under court challenge since its limited rollout in January, but a federal appeals court has allowed it to continue while considering its legality. The U.S. Court of Appeals for the 9th Circuit is not expected to issue a decision for weeks — possibly months — giving federal immigration officials time to return thousands of migrants from Central America, Cuba and other countries to Mexico in a bid to keep the migrants from residing in the United States.

Federal officials have returned 12,000 migrants to Mexico so far this year, according to data reviewed by The Washington Post. The U.S. government hopes to transfer thousands more under a June 7 agreement with Mexico that calls for that country to help facilitate the program south of the U.S. border.

“This policy is being implemented and being expanded and that’s not going to stop until the 9th Circuit rules,” said Judy Rabinovitz, a deputy director of the Immigrants’ Rights Project at the American Civil Liberties Union, which brought the lawsuit together with 11 Central American migrants and other groups. Plaintiffs filed a 74-page brief Wednesday urging the appeals court to immediately halt the program, “given the life-or-death stakes in this case.”

The MPP is one of the Trump administration’s last remaining levers to stem the historic surge of Central American families to the southern U.S. border, and the legal battle centers on one fundamental aspect of U.S. immigration law: the right to seek refuge in the United States.

Justice Department lawyers say in court papers that record numbers of migrant families are crossing the border illegally and filing largely meritless asylum claims because of the likelihood that they will be released into the United States with their children. Smugglers are advertising cut-rate trips to the border because the U.S. government cannot process the migrants’ cases quickly or detain children for very long. More than 144,000 migrants were taken into custody last month after crossing the southern border, the largest monthly total in more than a decade.

Ending the MPP “would impose immediate, substantial harm on the government’s ability to manage the crisis on our southern border,” government lawyers wrote.

The influx has swamped the immigration system. The U.S. Border Patrol has holding space for 4,000 people, and it had nearly 15,000 in custody this week. Immigration and Customs Enforcement has released more than 207,000 family members into the United States since December, ICE acting director Mark Morgan said this week.

While many migrants are fleeing violence and persecution in their homelands, others say they are escaping poverty and a lack of job opportunities, which are not grounds for obtaining U.S. asylum.

President Trump said immigration agents are planning to make mass arrests and deportations days after striking a deal with Mexico to curb the flow of migrants. (REF:Luis Velarde/The Washington Post)

The 9th Circuit has blocked a number of the Trump administration’s initiatives, including its attempt to ban asylum for all immigrants who enter the country illegally. But a three-judge panel allowed the MPP to continue in May while the court considers the legality of the policy. Two of the three appeals court judges expressed concern about the program, and a lower-court ruling found that federal law does not authorize the program.

One judge on the panel worried that U.S. border agents were sending migrants back to Mexico without asking them whether they feared being there, a step the judge said seemed “irrational.” Another said that existing law does not provide for the MPP and said the government is “clearly and flagrantly wrong.”

The ACLU and other plaintiffs said in court filings that U.S. officials are fundamentally reshaping the asylum system and sending migrants back to Mexican cities that have some of the highest murder rates in the world.

They said one plaintiff was kidnapped by a Mexican cartel, which “threatened to kill him and burn his body so no one could find him.” Mexican officials deported the pregnant wife of a Honduran minister who fled death threats. Another plaintiff reported repeated robberies by Mexican police.

“Every day that this program is allowed to remain in place, countless people are subjected to what amounts to one of the most abusive policies perpetrated on the U.S.-Mexico border,” said Shaw Drake, policy counsel for the ACLU Border Rights Center in El Paso. “Migrants have been kidnapped literally within minutes of return to Ciudad Juarez,” the Mexican city opposite El Paso on the Rio Grande.

Under MPP, asylum seekers who enter the United States are booked into custody and returned to Mexico with a court date weeks or months in the future, and officials issue migrants a list of pro-bono lawyers in the United States.

The Washington Post traveled to the Mexico-Guatemala border to see how Mexican authorities are trying to stem the flow of migrants. (The Washington Post)

U.S. Border Patrol agents do not ask migrants whether they fear returning to Mexico. Those who proactively declare that they are afraid are referred to trained asylum officers for interviews to determine whether they can stay in the United States.

Out of 12,000 people returned to Mexico under MPP, just 747 people expressed fear of returning to Mexico, said a U.S. asylum officer who spoke on the condition of anonymity to discuss the government program. Asylum officers sent most of those — 629 migrants — back to Mexico because the applicants must clear a high bar to prove that they are “more likely than not” to face a specific threat in Mexico.

“We’re making a good-faith effort to offer protection to people in danger, but it is so hard for them to meet the standard,” said Michael Knowles, president of the American Federation of Government Employees Local 1924, which includes asylum officers in Arlington, Va., the office that until now has handled most of the MPP cases. “Our officers fear that they’re going to be sending somebody back to danger. . . . We have officers who say, ‘I feel morally and ethically compromised.’ ”

The asylum officer said the main problem applicants encounter is that they can’t identify specific threats to them in Mexico.

The MPP is operational in the San Diego and El Centro sectors in California and the El Paso Border Patrol sector, which covers West Texas and the entire state of New Mexico. Arizona is likely to see MPP activity soon.

Asylum officers across the country will conduct remote interviews of applicants: Officers in San Francisco will handle Arizona cases, Los Angeles-based asylum officers will take California cases, and the Arlington, Va., office will cover Texas and New Mexico. Some asylum officers are now dedicated to MPP full time.

Officials are attempting to extend the program along the nearly 2,000-mile border but are giving Mexico time to expand its shelter capacity, a top official at U.S. Customs and Border Protection said.

The Trump administration’s policies are wearing on asylum officers, who are being required to train CBP officers to handle asylum screenings. The acting director of U.S. Citizenship and Immigration Services, Ken Cuccinelli, caused an uproar this week by sending a pointed email to asylum officers scolding them for approving 80 percent of initial asylum applications when most cases are rejected in court.