WASHINGTON (AP) — Former Trump adviser Peter Navarro revealed in a draft court filing Tuesday that he has been subpoenaed to appear before a grand jury this week as part of the Justice Department’s sprawling probe into the deadly insurrection at the U.S. Capitol.

Navarro, who was a trade adviser to then-President Donald Trump, said Tuesday that he was served by the FBI at his Washington, D.C., house last week. The subpoena is the first known instance of prosecutors seeking testimony from someone who worked in the Trump White House as they investigate the worst attack on the Capitol in two centuries.

In an 88-page draft filing, Navarro claims the House select committee investigating the Jan. 6, 2021, Capitol attack is unlawful and therefore a subpoena it issued to him in February is unenforceable under law. The 72-year-old said he was planning on filing the claim against the committee, Speaker Nancy Pelosi, D-Calif., and the U.S. attorney for D.C., Matthew M. Graves, on Tuesday.

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A spokesman for the Department of Justice did not immediately respond to a request for comment Tuesday.

Though the scope of the department’s investigation remains unclear, the subpoena to Navarro could signal that the department is widening its probe to examine the activities and records of people who worked directly for the Republican president. The department previously issued subpoenas to people connected to the Jan. 6 attack and the rallies in Washington that preceded the violence, in which a mob loyal to Trump stormed the Capitol in a brazen bid to overturn the 2020 presidential election and keep Democrat Joe Biden from replacing Trump in the White House.

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The subpoena also comes as pressure continues to mount on the Justice Department and Attorney General Merrick Garland to consider prosecuting Trump since the Jan. 6 House committee laid out an argument for what its members believe could be a viable criminal case against the former president.

Garland has given no public indication about whether prosecutors might be considering a case against the former president. He has, though, vowed to hold accountable “all January 6th perpetrators, at any level” and has said that would include those who were “present that day or were otherwise criminally responsible for the assault on our democracy.” Roughly 300 people have pleaded guilty to crimes stemming from the riot, including seditious conspiracy and assault.

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The subpoena from federal prosecutors also comes months after Navarro, a former economics professor, received a congressional subpoena from lawmakers investigating the Jan. 6 attack. Members of the select committee sought testimony from Navarro about his public efforts to help Trump overturn the election, including a call after the 2020 presidential election persuading state legislators to join their efforts.

Navarro has refused to cooperate with the committee, and he and fellow Trump adviser Dan Scavino were found in contempt of Congress in April.

Members of the committee made their case at the time that Scavino and Navarro were among just a handful of people who had rebuffed the committee’s requests and subpoenas for information. The panel has interviewed more than 1,000 witnesses about the insurrection and is preparing for a series of hearings to begin next week.