The congressional committee investigating the Jan. 6 insurrection has turned its sights on yet another fellow legislator, this time requesting that Rep. Jim Jordan turn over any communications he had with former President Donald Trump and those who sought to upend the election.

In a letter made public Wednesday, the bipartisan committee requested Jordan’s “voluntary cooperation” in its ongoing mission to examine who was behind the violence on Jan. 6—and explore what role the Trump White House played in trying to stage a coup.

Jordan’s congressional office did not immediately respond to a request for comment.

Jordan (R-OH) drew curiosity back during a House Rules Committee meeting in October when he asserted that he had communicated with Trump after the insurrection, but not during the attack on the U.S. Capitol building. However, members of the panel have said they do consider Jordan, a longtime Trump ally and former White House Chief of Staff Mark Meadows’ closest friend in Congress, a potentially significant witness to the events that day.

Jordan has already shown up in one key text message to Meadows that the committee released. In that text, Jordan quoted from a document laying out a plan to overturn the election. While the committee didn’t initially disclose that it was Jordan who had sent the text to Meadows, Jordan later acknowledged to a right-wing media outlet that it was him.

The committee’s request is not a subpoena, so the congressman is not compelled to show up and testify behind closed doors or deliver documents, as others have done. But today’s move could be the first step in the process, as the committee has taken increasingly harsh measures against witnesses who refuse to cooperate with its investigation.

The panel has already voted to hold three witnesses in contempt: one-time White House adviser Steve Bannon, ex-Justice Department official Jeffrey Clark, and Meadows, Trump’s former chief of staff.

Earlier this week, the panel sent a similar letter to Rep. Scott Perry (R-PA), after it said members got information from witnesses “tying Rep. Perry” to Jan. 6, including evidence proving “his involvement in efforts to install former Department of Justice official Jeffrey Clark as acting Attorney General.”

AJ McDougall contributed to this story.