The letter was sent Thursday to Attorney General William Barr. It was signed by nine Democratic members of the Senate Judiciary Committee, including Sheldon Whitehouse of Rhode Island, Richard Durbin of Illinois, Mazie Hirono of Hawaii and Amy Klobuchar of Minnesota. They are requesting extensive information about the department's hiring practices for trial-level and appellate judges, among other documents.

The Justice Department did not immediately respond to a request for comment on the letter.

The senators' concerns echo those voiced by former and current immigration judges, including the head of the union representing those judges. Ashley Tabaddor, the president of the National Association of Immigration Judges, testified at a House Judiciary Committee hearing last month that immigration courts should no longer be overseen by the Justice Department.

"The only real and lasting solution is the establishment of an independent Immigration Court," Tabaddor wrote in her testimony. She also wrote: "It must be free from the constantly changing (often diametrically opposed) politicized policy directives of the Department of Justice."

The judge's union has pushed back against productivity quotas for immigration judges, which were announced in 2018. The union also opposed new Trump administration rules that gave more power to the director of the Executive Office for Immigration Review, a political appointee.

The Trump administration, for its part, has moved to decertify the judges' union.

Immigration courts face a massive backlog of more than a million cases. And there's wide agreement that the court system needs reform. But not everyone believes that removing immigration courts from the Justice Department is the right approach.

"The attorney general and his subordinates are actively working to remedy this problem, by providing the needed resources to the immigration courts," wrote Andrew Arthur, a former immigration judge who is now a fellow at the Center for Immigration Studies, in his testimony before the House Judiciary Committee last month. "Restructuring the immigration courts ... will almost certainly not address the core problems that are facing those courts," Arthur added.

At a time when caseloads are surging, some immigration judges are quitting, citing frustration and exhaustion. Judge Charles Honeyman retired from the Philadelphia Immigration Court in January after 24 years on the job.

"I would want future administrations and the Congress to think of immigration judges as judges, literally, and give them the autonomy and the independence and the confidence to make decisions without political interference or overreach," he said in an interview with NPR's Noel King.

"The only way to do that is to create an independent court where the judge makes a decision and the judge isn't afraid of how many cases he has to complete for the year or whether some political actor is going to be looking over his shoulder and say, 'I don't agree with that decision. We're going to find a way to put pressure on you,' " Honeyman said.

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