John Gore, a top official in the Justice Department’s Civil Rights Division, will not appear for a deposition scheduled for tomorrow with the House Committee on Oversight and Reform, according to a letter the Justice Department sent the committee chairman on April 24.

Stephen Boyd, the department’s top Hill liaison, wrote in the letter, which The Daily Beast obtained, that Gore will not appear as long as Chairman Elijah Cummings blocks him from bringing along lawyers from the Justice Department.

“We are disappointed that the Committee remains unwilling to permit Department counsel to represent the interests of the Executive Branch in the deposition of a senior Department official,” Boyd wrote. “Accordingly, Attorney General Barr’s determination that Mr. Gore will not appear at the Committee’s deposition unless a Department attorney may accompany him remains in effect.”

The committee wants to question Gore about his role in the Trump administration’s effort to add a question to the 2020 Census about citizenship. The committee authorized a subpoena of Gore earlier this month. His refusal to participate in a deposition may result in an effort by the committee to hold him in contempt.

“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,” said Kerri Kupec, a department spokesperson.

A spokesperson for Cummings did not immediately respond to a request for comment.

Gore will be the highest-profile Trump administration official to defy a Congressional subpoena—so far. Earlier this week, the lawyer for Carl Kline, a career official who green-lit Jared Kushner’s security clearance, told Cummings he will not participate in a deposition about that issue unless lawyers from the White House Counsel’s Office can attend. Cummings has taken steps to hold him in contempt of Congress. If the House votes to hold him in contempt—a safe bet—then they may refer the matter to the D.C. U.S. Attorney. That attorney is Jessie Liu, a Trump appointee.

Gore will find himself in a similar situation if the House votes to hold him in contempt.

These cases will test the power of Congressional committees. In the past, efforts to compel testimony have garnered mixed results; House Republicans famously voted to hold then-Attorney General Eric Holder in contempt in 2012 while investigating the Fast and Furious scandal. Despite the contempt vote, Holder still didn’t comply with the House’s demands.

The census investigation is of paramount importance to Democrats, who argue the question about the citizenship will discourage participation. Less participation could result in millions of people not being counted, they argue; and undercounting could mean a mis-apportionment of Congressional districts and lower levels of federal funding to communities that are underrepresented. Republicans, meanwhile, argue the federal government has asked about citizenship in the past and that it won’t result in unfairness.

Democrats and other opponents of the citizenship question, including multiple civil rights groups, sued to keep it from appearing on the census. The Supreme Court heard oral arguments on that litigation earlier this week. Observers have guessed that the Court will lean in the direction of allowing the question.