A coalition of American asylum officers urged a federal court to block the Trump administration from returning some migrants seeking refuge in the U.S. to Mexico, saying the policy was “contrary to the moral fabric of our Nation.”

The American Federation of Government Employees Local 1924 — a union that represents thousands of government employees, including asylum officers — directly targeted the White House’s “remain in Mexico” policy in a brief it filed with the 9th U.S. Circuit Court of Appeals. The provision, which the Trump administration enacted in January, has forced thousands of people seeking asylum to wait on the Mexican side of the border while their applications for refuge are processed.

“By forcing a vulnerable population to return to a hostile territory where they are likely to face persecution, the [Migrant Protection Protocols] abandons our tradition of providing a safe haven to the persecuted and violates our international and domestic legal obligations,” the union wrote in the friend-of-the-court brief.

The letter points to previous policies that allowed asylum-seekers to wait in the United States while their applications were pending, noting: “The system has been tested time and again, and it is fully capable … of efficiently processing asylum claims.”

The Washington Post was the first to report on the brief.

The Trump administration policy has faced heavy criticism from human rights groups and Democratic lawmakers, as well as a bevy of lawsuits. A federal district judge in San Francisco initially blocked the provision in April, but upon appeal, the 9th Circuit ruled just days later that it could go forward while the case worked its way through the court system. The judges issued an extension on their earlier order last month.

The union brief represents a dramatic break with official policy by many officers tasked with enacting the White House’s will. In the filing, the union argued that many employees were “duty bound to protect vulnerable asylum seekers” and should not be “forced to honor departmental directives that are fundamentally contrary to the moral fabric of our nation.”

“Under the MPP, they face a conflict between the directives of their departmental leaders to follow the MPP and adherence to our Nation’s legal commitment to not returning the persecuted to a territory where they will face persecution,” the union wrote.

Many of those seeking asylum in the U.S. are escaping violence in Central America. The union said that Mexico was simply “not safe” for most of the asylum-seekers, pointing to reports of kidnappings for ransom, human rights abuses and gang violence. The U.S. State Department has also acknowledged that migrants seeking asylum are likely no safer waiting in Mexico than they would be in the countries they initially fled.

The Mexican government said that as of this week, more than 15,000 people had been sent back to the country under Trump’s policy. The White House has moved to aggressively combat the number of people seeking refuge in the United States, and critics say the revamped “remain in Mexico” policy was meant to deter potential asylum-seekers.

The Post notes that the Justice Department has argued many migrants have filed bloated claims to seek asylum simply to gain access to the U.S. for months or years while they wait for a court to rule on their applications. Former Department of Homeland Security Secretary Kirstjen Nielsen claimed many people have “disappeared into the United States” once they crossed the border.

However, DOJ statistics show that more 90 percent of asylum-seekers fulfilled their court obligations between 2013 and 2017.

Read the full letter below: