Donald Trump attempted to contact one of the witnesses who has been speaking to the House select committee investigating the January 6 insurrection, the panel said Tuesday.

Liz Cheney, the Republican vice-chair of the panel, delivered the revelation at the conclusion of the committee’s seventh public hearing on the Capitol attack.

According to Cheney, Trump tried to call the unnamed witness after the committee’s sixth hearing last month. The witness, who has not yet been publicly revealed as a participant in the committee’s investigation, declined the call.

Instead, the witness informed their lawyer about Trump’s attempt to contact them. The lawyer then informed the January 6 committee about the call, and investigators passed the information along to the justice department.

“Let me say one more time: we will take any efforts to influence witness testimony very seriously,” Cheney said.

If the justice department gathers evidence indicating that Trump was attempting to influence witness testimony in the January 6 investigation, prosecutors could pursue criminal charges against the former president.

This is not the first time that the issue of witness intimidation has been raised in connection to the select committee’s work. At the committee’s sixth hearing, Cheney revealed that at least two witnesses said they had been contacted by Trump allies urging them to stay loyal to the former president when speaking to investigators.

One witness told the committee: “What they said to me is, as long as I continue to be a team player, they know that I’m on the right team. I’m doing the right thing, I’m protecting who I need to protect. … They have reminded me a couple of times that Trump does read transcripts and just to keep that in mind as I proceed through my depositions and interviews with the committee.”

Cheney said the evidence of possible witness intimidation “raises significant concern”, and she promised that the committee would investigate the matter further.

“I think most Americans know that attempting to influence witnesses to testify untruthfully presents very serious concerns,” Cheney said last month. “We will be discussing these issues as a committee, carefully considering our next steps.”