Immigrants take the oath of allegiance to the United States at a naturalization ceremony on Feb. 2, 2018, in New York City. Congressional Democrats have asked the federal government to eplain why there is a massive backlog of immigration cases. (John Moore/Getty Images)

More than 80 Democratic members of Congress have asked the Government Accountability Office to conduct an investigation into the “record-breaking” backlog of immigration cases pending under the Trump administration.

“Processing delays for applications and immigration benefits have reached crisis levels and these delays are hurting families and businesses that depend on timely adjudications,” Rep. Joaquin Castro (D-Tex.) and 81 other lawmakers wrote in a letter, submitted Friday to Comptroller General Gene Dodaro. The Washington Post obtained a copy of the letter Friday.

The lawmakers specifically criticized U.S. Citizenship and Immigration Services, saying they are “alarmed” that the agency “is adjudicating cases at an increasingly slow pace compared to previous years.”

The Trump administration, which last month detained 109,144 migrants along the southern border with Mexico, has spent the past two and a half years struggling to win congressional approval for legislation that would expand a wall on the southern border and dramatically alter the system through which foreign nationals are admitted to the United States.

President Trump and his advisers have called for a “merit-based” immigration system that would make paths to U.S. residency and citizenship contingent on specific skill sets.

Immigration attorneys, advocates and Democratic lawmakers say the administration has intentionally slowed the process through which it grants citizenship and other immigration benefits, creating a massive backlog.

“The wait times for citizenship have become outrageous,” Castro said in an interview Friday, noting that his concern is that the White House is taking steps to “stop certain people from becoming citizens and staying in this country.”

Jessica Collins, a spokeswoman for USCIS, said that many factors can affect processing times but that “waits are often due to higher application rates rather than slow processing.”

The agency, Collins said in an email, has expanded its field offices and hired more staff to keep pace with the “extraordinary demand” for services.

“USCIS strives to adjudicate all applications, petitions, and requests as effectively and efficiently as possible in accordance with all applicable laws, policies, and regulations,” she said.

The USCIS net backlog — which includes all immigration case applications, ranging from pending green cards to immigrant work visas — exceeded 2.3 million cases by last fall, a recent analysis by the American Immigration Lawyers Association found.

Permanent residents who apply for citizenship can now wait more than two and a half years for their application to be processed, the members of Congress said in their letter, citing the association’s findings.

That has happened despite the increase in staffing and officers, they wrote. And although USCIS “has an extended history” of backlogs, it hasn’t seen a slowdown this extreme since the aftermath of the Sept. 11, 2001, terrorist attacks, when the administration of President George W. Bush introduced new security measures.

“We haven’t seen a satisfactory explanation for why processing times would spike so high in such a short amount of time,” Castro said.