Lawmakers running the House impeachment inquiry have invited former national security adviser John Bolton to provide testimony next Thursday.
The deposition notice, obtained by NPR, notes that it requests a "voluntary appearance."
The notice will likely not be enough to compel Bolton to testify.
Bolton is represented by the same lawyer as former deputy national security adviser Charles Kupperman, who has filed a lawsuit to determine whether he has to testify to the committees despite a subpoena.
A spokesperson for Bolton declined to comment. Bolton is expected to testify only if a subpoena compelling his testimony is upheld by the courts, according to a source familiar with his legal strategy.
Lawmakers from the House Intelligence, Foreign Affairs and Oversight committees are eager to hear from the former Trump aide.
"John Bolton is a very important witness ... he has very relevant information and we do want him to come in and testify," said House Intelligence Committee Chairman Adam Schiff on ABC this past weekend. "My guess is that [the White House] is going to fight us having John Bolton in."
As Trump's third national security adviser, Bolton had a front-row seat to the Trump administration's policies toward Ukraine, which forms a central part of the House's impeachment inquiry.
Fiona Hill, a former White House aide, had previously testified to Congress that Bolton had been distressed about the administration's direction on Ukraine.
In particular, Hill said that Bolton worried that Trump's personal lawyer Rudy Giuliani had created a back-channel for communications with the Ukrainian government. According to Hill, Bolton had said that Giuliani was "a hand grenade who is going to blow everybody up."