Washington — Citing the American government's refusal to take in a group of desperate Jewish refugees fleeing Nazi Germany on the eve of World War II, a group of current asylum officers tasked with overseeing the controversial "Remain in Mexico" policy asked a federal appeals court in a surprising legal filing late Wednesday to block the Trump administration from implementing it.

The labor union representing thousands of asylum officers, Local 1924, filed the extraordinary court filing siding with plaintiffs seeking to prevent the Department of Homeland Security (DHS) from implementing the so-called "Remain in Mexico" program. Under the policy, officially called the Migrant Protection Protocols (MPP), migrants who claim asylum at U.S. ports of entry along the southern border are required to wait in Mexico while their cases are adjudicated in American immigration courts.

In the filing to the Ninth Circuit Court of Appeals — which is reviewing the legal challenge to "Remain in Mexico" brought by the American Civil Liberties Union (ACLU) and other plaintiffs — the union of asylum officers said the program violates U.S. and international law because it places asylum seekers in dangerous circumstances.

Get Breaking News Delivered to Your Inbox

"By forcing a vulnerable population to return to a hostile territory where they are likely to face persecution, the MPP abandons our tradition of providing a safe haven to the persecuted and –– violates our international and domestic legal obligations," the amicus brief read.

Asylum officers, the filing argued, "should not be forced to honor departmental directives that are fundamentally contrary to the moral fabric of our Nation."

DHS did not immediately respond to CBS News' request for comment.

Central American migrants, who are waiting for their court hearing for asylum seekers that returned to Mexico to await their legal proceedings under a new policy established by the U.S. government, are seen at a migrant shelter in Ciudad Juarez, Mexico June 10, 2019. Picture taken June 10, 2019. JOSE LUIS GONZALEZ / REUTERS

The remarkable rebuke of the "Remain in Mexico" policy by the very same civil servants carrying it out could prove to be a significant blow to the administration's legal and political defense of the program, which the White House is betting on to curb an unprecedented surge in Central American families heading towards the U.S.-Mexico border.

The Trump administration has begun to accelerate the "Remain in Mexico" policy in the three locations where officials are currently carrying it out: the California border cities of San Diego and Calexico and El Paso, Texas. Over approximately two weeks, U.S. authorities have turned back about 5,000 asylum seekers at these three ports of entry, bringing the total number of migrants returned to Mexico to more than 15,000, according to figures by the Mexican government.

The administration is betting that the expansion will send a powerful message of deterrence to people in Central America considering undertaking the perilous journey north. Even if they arrive at the U.S. border and seek asylum, this line of reasoning goes, they will likely be forced to wait in Mexico for months while their cases are adjudicated.

But the asylum officers said the recent filing that "Remain in Mexico" is "entirely unnecessary" and not designed to stem the current large-scale flow of migration from Central America. They argued the U.S. immigration system has been "tested time and again" and is capable of efficiently processing asylum claims if it has the adequate resources to do so.

"The MPP, contrary to the Administration's claim, does nothing to streamline the process, but instead increases the burdens on our immigration courts and makes the system more inefficient," the officers wrote.

Echoing concerns raised by immigrant advocates and attorneys since the Trump administration policy was first implemented, the union said the policy violates the "non-refoulement" standard in domestic and international law, principally because it returns vulnerable populations to Mexico. The filing specifically cites the precarious conditions pregnant women, families with children, LGBT individuals and members of indigenous communities face in Mexico.

"The administration of the MPP results in a violation of the nonrefoulement obligation because, under the MPP, individuals whose lives and freedoms would be threatened on the basis of their race, religion, nationality, political opinion, or membership of a particular social group in Mexico, or who would be in danger of being subjected to torture in Mexico, will be returned to Mexico," the officers wrote.

Customs and Border Protection (CBP) officials are typically the first to encounter migrants at both at ports of entry along the border and between them. The CBP officials are supposed to ask migrants if they fear returning where they came from. If migrants say yes, they are then referred to undergo so-called "credible fear interviews" with asylum officers, who work for United States Citizenship and Immigration Services (USCIS), another branch of DHS. If the migrants pass the credible fear test, they can formally apply for asylum in the immigration court system.

Under the "Remain in Mexico" policy, however, CBP officials do not ask migrants who claim asylum if they fear returning to Mexico. Instead, a migrant needs to say, without being asked, if he or she fears persecution in Mexico. The union said this is something Central American migrants will likely not do because they do not yet know that they may face persecution in Mexico, as they were there just briefly in their journey to the U.S.

Even if the migrants spontaneously indicate they fear persecution in Mexico, the asylum officers said in the filing that the credible fear tests under this policy's guidelines are almost impossible to satisfy, prompting them to require migrants to wait in Mexico while their cases are adjudicated.

"It imposes a significantly higher evidentiary standard previously reserved for a full-scale hearing before an immigration judge," the officers wrote, referring to the new credible fear interview. "This mismatch between the high evidentiary standard and the inadequate procedures all but ensures violation of the non-refoulement obligation."

On Twitter, the recently appointed acting director of USCIS Ken Cuccinelli, a notorious immigration hardliner, accused "complaining" union leaders — his own employees — of denying the reality at the U.S.-Mexico border.

"This lawsuit is an attempt by the union to score short-term political points. Our ability to provide humanitarian relief to those who lawfully qualify for it will collapse under this influx of fraudulent and non-meritorious claims," he wrote.

This demonstrates the complaining union leaders are choosing to deny reality. Our system is broken. Even Democrats now admit we are in a crisis. But not the union... — USCIS Acting Director Ken Cuccinelli (@USCISCuccinelli) June 27, 2019

Citing a report by the State Department, the union noted there's widespread impunity for human rights abuses in Mexico. It also accused the Mexican government of not keeping its promise to protect migrants returned under "Remain in Mexico."

The officers noted that the U.S. asylum system built in the wake of World War II and subsequent years is "highly respected internationally" for being compassionate, while at the same time enforcing laws, cracking down on fraud and safeguarding national security. The migrant policy, they said, abandons the commitment the U.S. has made to people around the world who've been displaced by conflict, ethnic strife and natural disasters during the last decades.

"Now, perhaps more than ever, America needs to continue its longstanding tradition of offering protection, freedom, and opportunity to the vulnerable and persecuted," the filing read. "Forty-nine members of the amicus curiae signed up to be asylum and refugee officers to help our nation fulfill that commitment. They did not sign up to administer the MPP."