Attorney General William P. Barr speaks about the release of a redacted version of special counsel Robert S. Mueller III’s report during an April 18 news conference at the Justice Department in Washington. (Patrick Semansky/AP)

The Justice Department said Wednesday that it will not comply with a congressional subpoena for a Trump administration official to testify in a House panel’s investigation of the addition of a citizenship question to the 2020 Census.

In a letter to the House Oversight and Reform Committee, Assistant Attorney General Stephen E. Boyd informed the panel that John Gore, the principal deputy assistant attorney general for the Justice Department’s civil rights division, will not give a deposition.

Gore’s refusal to appear before the committee is at the direction of Attorney General William P. Barr, according to the letter, escalating the already explosive fight between the executive and legislative branch.

Boyd said the reason Gore would not appear stemmed from the panel’s refusal to allow a department attorney to join him for the deposition. Rep. Elijah E. Cummings (D-Md.), chairman of the committee, has threatened to hold Gore in contempt if he does not show.

In a statement Wednesday, Cummings said committee investigators would press ahead with the deposition Thursday morning and hoped Gore would appear.

“As an officer of the court and a senior lawyer in a position of public trust at the Department of Justice, Mr. Gore should be well aware of his constitutional, legal, and ethical obligations to comply with a duly authorized subpoena from Congress,” Cummings said. “Those obligations have not been erased by the attorney general or the president.

The development comes just hours after President Trump told The Washington Post in an interview that he opposes current and former White House aides providing testimony to congressional panels, calling it unnecessary after the White House cooperated with special counsel Robert S. Mueller III’s probe of Russian interference in the 2016 election and the president’s own conduct in office.

“There is no reason to go any further, and especially in Congress where it’s very partisan — obviously very partisan,” Trump said.

Barr’s decision to block Gore’s testimony comes a day after the White House blocked a top security clearance official from testifying for the Oversight panel’s probe of the security clearance process. Cummings announced that he would hold the official, Carl Kline, in contempt of Congress in the coming days.

The committee is investigating the administration’s plan to add a citizenship question to the 2020 Census despite evidence it could lead to an undercount of millions of people. Officials estimate that about 6.5 million people probably would be affected in states and urban areas with large Hispanic and immigrant populations, places that tend to vote for Democrats.

The decennial count of the nation’s population determines the size of each state’s congressional delegation, the number of votes it receives in the electoral college and how the federal government allocates hundreds of billions of dollars.

The Supreme Court is considering a challenge to the administration’s planned change to the census.

Kerri Kupec, spokesman for the department, said Wednesday, “In keeping with longstanding Department of Justice policy, neither Mr. Gore nor anyone else in the Department will be forced to testify in their capacity as a DOJ official on DOJ matters without DOJ counsel.”

A DOJ official later argued that the panel “has provided no legitimate or constitutional basis for excluding a DOJ lawyer from assisting at the deposition” but also said if a department lawyer may appear with Gore, Barr “will allow the deposition to go forward.”