A top aide to Vice President Mike Pence who was on the July phone call between President Trump and his Ukrainian counterpart is expected to testify Thursday in the House impeachment inquiry.

Jennifer Williams also accompanied the vice president when he traveled to Poland in September and met with Ukrainian President Volodymyr Zelensky about the nearly $400 million in military assistance that had been put on pause by the White House.

She would be the first person from Pence’s office to testify in the probe.

Her lawyer, Justin Shur, told CNN that Williams would testify “if required to appear.”

“Jennifer is a longtime dedicated State Department employee,” Shur said. “If required to appear, she will answer the committees’ questions. We expect her testimony will largely reflect what is already in the public record.”

The White House has been discouraging staffers from appearing before the combined House panels, but some have voluntarily appeared.

The July 25 phone call between Trump and Zelensky, first revealed in a whistleblower’s complaint, is at the center of the impeachment inquiry.

Democrats allege that Trump abused the power of his office by dangling the millions in aid to Zelensky in return for Ukraine investigating the president’s political rival Joe Biden.

House Speaker Nancy Pelsoi launched the inquiry in September and House committees have been hearing testimony in a closed-door setting from a number of former and current diplomats and administration officials in the weeks since.

But on Wednesday, Rep. Adam Schiff, the chairman of the House Intelligence Committee, announced that televised hearings would begin next Wednesday.

Schiff, a California Democrat spearheading the impeachment efforts, said acting US Ambassador to Ukraine William Taylor will appear next Wednesday along with Deputy Assistant Secretary of State George Kent.

Former US Ambassador to Ukraine Marie Yovanovitch will testify on Friday.