House Democrats on Friday sent a letter to Vice President Mike Pence demanding his office turn over documents related to Ukraine as part of their formal impeachment inquiry.

NEW: House Democrats seek Ukraine-related documents from VP Pence as part of impeachment inquiry. – @AlexNBCNews pic.twitter.com/ANp5IOT8Yo — NBC Politics (@NBCPolitics) October 4, 2019

In the letter, the chairmen of the House Intelligence, Oversight and Reform, and Foreign Affairs Committees request that the vice president turn over the records by October 15th.

“Recently, public reports have raised questions about any role you may have played in conveying or reinforcing the President’s stark message to the Ukrainian President,” the letter states.

“Your failure or refusal to comply with the request, including at the direction of or behest of the president or the White House, shall constitute evidence of obstruction of justice of the House’s impeachment inquiry and may be used as an adverse inference against you and the president,” it continues.

The development comes after House Democrats on Wednesday threatened to subpoena White House officials for records on President Donald Trump’s discussions with the leader of Ukraine, which a partisan CIA officer alleged in a so-called “whistblower” complaint that included pressure from President Trump for Ukrainian President Volodymyr Zelensky to investigate Hunter Biden, the son of former Vice President and 2020 White House contender Joe Biden.

As Breitbart News reported earlier this year, Biden forced out former Ukrainian prosecutor Viktor Shokin as he was investigating an energy company called Burisma Holdings, which was paying Biden handsomely as a member of its board. The former vice president even boasted to the Council of Foreign Relations last year that he had threatened to withhold $1 billion in U.S. aid unless the prosecutor was fired. (He did not tell the audience about his son’s role.) Conservatives claim Biden obstructed justice to protect his son — who enriched himself using his father’s prestige.

President Trump and Zelensky have denied any pressure to look into the Biden family was applied and the White House, in a nod to transparency, released the transcript of leaders’ July 25th conversation last week.

“I think you read everything. I think you read text. I’m sorry, but I don’t want to be involved to democratic open elections, elections of USA. No, sure, we had I think good phone call. It was normal. We spoke about many things, and I — so I think and you read it that nobody pushed me,” Zelensky told reporters at the United Nations in New York City last week.