MILWAUKEE (CN) — The most powerful Republican in the Wisconsin Legislature on Sunday sued the U.S. House of Representatives’ committee investigating the Jan. 6, 2021, attack on the U.S. Capitol by a mob of Donald Trump supporters to enjoin the committee from forcing him to testify regarding a conversation he had with Trump this summer about overturning the 2020 election results.

The subpoena and accompanying letter served to Wisconsin Assembly Speaker Robin Vos on Saturday seeks Vos’ testimony about a phone call he had with Trump in July “in which Mr. Trump asked you to take measures to change the result of the 2020 presidential election in Wisconsin,” according to the letter.

The letter claims the call was made in response to a July ruling from the Wisconsin Supreme Court banning the use of most absentee ballot drop boxes in the state but stopping short of saying ballots cast using them were illegal.

As the committee’s letter notes, that call allegedly ended with Vos telling Trump the Wisconsin Constitution does not allow for the kind of broad reversal of election results he wants. Trump responded, the letter says, by posting derogatory statements about Vos on the former president’s Truth Social platform and endorsing Vos’ GOP opponent in August primaries, a challenge Vos narrowly survived.

“The circumstances and details regarding your interactions with former President Trump related to the 2020 election are relevant to the Select Committee’s investigation and proposed recommendations,” concludes the letter signed by Congressman Bennie Thompson of Mississippi, chairman of the House Jan. 6 committee.

The committee—formally known as the U.S. House Select Committee to Investigate the January 6th attack on the United States Capitol—formed and began its investigation in the summer of 2021, and to date it has conducted more than 1,000 interviews, held multiple public hearings and issued dozens of subpoenas to everyone from Trump administration officials and nongovernmental Trump allies, to those specifically tied to the U.S. Capitol attack and sitting members of Congress aligned with the former president.

Vos’ subpoena commanded that he sit for a deposition at the U.S. Capitol in Washington or via videoconference at 10 a.m. Monday morning.

However, in the less than 48 hours between being served his subpoena and the scheduled time for his deposition, Vos sued the Jan. 6 committee and Thompson in Milwaukee federal court, claiming that the subpoena poses an undue burden and the committee itself is improperly constituted, in part because it has only nine members and none of them were appointed after consultation with House Minority Leader Kevin McCarthy of California, who the committee has also subpoenaed.

Despite knowing for months about Vos’ call with Trump, the committee put such short time constraints on the lawmaker’s deposition because it wants to edit his testimony for a multimedia show at its next televised hearing on Wednesday, the lawsuit alleges.

Far from wanting to question Vos about the actual breach at the Capitol or the events leading up to it, the complaint states, “the Committee is demanding Speaker Vos appear for a deposition to answer questions irrelevant to the Committee’s investigation, with virtually no notice, in the closing days of his reelection campaign, merely because of the Committee’s public relations scheme.”

The Wisconsin Republican’s complaint additionally charges that the subpoena violates his immunity as a state lawmaker from civil process in federal court and falls beyond the Jan. 6 committee’s authorized topics of investigation. The filing seeks a temporary restraining order preventing the committee from enforcing its subpoena, then a declaration that the whole subpoena is invalid and a permanent injunction blocking its enforcement.

Vos is represented in his lawsuit by Matthew Fernholz with the Cramer, Multhauf & Hammes firm based in Waukesha, Wisconsin, as well as Nashville-based civil rights attorney Adam Mortara and Edward Greim, a partner at the Graves Garrett firm in Kansas City.

In the complaint, Vos and his counsel claim “the committee’s actions in issuing the subpoena to Speaker Vos demonstrate the committee has lost all sense of boundaries,” painting the committee as a politically motivated outfit gone rogue in its hounding of a former president it considers a partisan enemy.

“Put simply, the committee views itself as having a roving commission to examine any matter involving its political adversaries that piques its interest without any regard for the rights of the citizens subjected to its investigation,” the complaint says. “The court must quash this subpoena and remind the committee that it, like all other government entities, is subject to limitations on its powers.”

Vos’ lawsuit is docketed in the court of Chief U.S. District Judge Pamela Pepper, a Barack Obama appointee, and a scheduling conference is set for Tuesday afternoon, according to court records.

Staff with the Jan. 6 committee could not be immediately reached for comment on Vos’ lawsuit and the status of his deposition on Monday. Vos’ office also could not be reached.

Vos used his legislative authority last year to appoint former Wisconsin Supreme Court Justice Michael Gableman to spearhead an investigation into alleged fraudulent voting and other improprieties in the state’s 2020 election, the third of three independent reviews of the contest, which resulted in a 21,000-vote victory for President Joe Biden.

The subject of numerous lawsuits and delays, the investigation—which resulted in its head suggesting the legally dubious decertification of Wisconsin’s election results and broadcasting fringe conspiracy theories over the 2020 presidential contest—was ultimately scrapped in late August after more than a year in which more than $1 million in taxpayer money was spent and no findings of widespread fraud turned up. This occurred a couple of weeks after Vos fired Gableman, who turned on Vos to endorse his bested primary challenger alongside Trump.