Williams’ lawyer interrupted the testimony after Congressman Adam Schiff asked Williams if there was anything in the call that is relevant to the House of Representatives impeachment probe of President Donald Trump.
"As we previously discussed with both majority and minority staff of the committee, the office of the vice president has taken the position that the September 18 call is classified," the lawyer said. "Given the position of the vice president’s office on classification, I’ve advised Ms. Williams not to answer further questions about that call in an unclassified setting."
Williams then agreed to answer Schiff’s question in a classified hearing or in writing.
In October, Mike Pence told reporters he would not object to releasing transcripts of his past phone calls with Ukrainian President Volodymyr Zelensky.
The inquiry was initiated after a whistleblower sent a complaint to Congress, saying Trump pressed Zelensky to investigate possible corruption by 2020 Democratic presidential candidate Joe Biden and his son Hunter Biden and allegedly threatened to withhold US aid to Ukraine.
Trump denied the allegations calling them another attempt at a political witch hunt to reverse the outcome of the 2016 US presidential election, and published the transcript of the telephone call with Zelensky, which did not contain any signs that the US president overtly threatened to withhold financial assistance to Ukraine.