House committees leading the impeachment inquiry against President Trump requested documents on Friday from Vice President Mike Pence to examine the extent of his participation in or knowledge of Trump's actions while he allegedly pressured the Ukrainian president to investigate Joe Biden and his son.

The big picture: The committees are requesting these documents by Oct. 15 — if Pence fails to comply, a subpoena will follow. Per Axios' reporting, the White House is planning to send Speaker Nancy Pelosi a letter arguing that Trump and his team can ignore lawmakers' demands until she holds a full House vote formally approving an impeachment inquiry.

Highlights of what the committees are requesting:

Documents relating to Trump's July 25 phone call with Ukrainian President Volodymyr Zelensky and the identity of who listened, participated in or reviewed the call.

Communications between current and former White House officials, Justice Department officials, and others on that phone call and other communication between Trump and Zelensky.

Documents relating to Pence's Sept. 18 call with Zelensky.

What they're saying: Katie Waldman, Pence's press secretary, confirmed to NBC News that the vice president's office received the letter on Friday and said that it did not appear to be a serious request, "given the scope" of it.

Go deeper: Trump letter dares Pelosi to hold vote on impeachment inquiry