House Democrats are threatening to subpoena the White House in their fight for more documents related to President Trump’s July phone call with Ukrainian President Volodymyr Zelensky.

The chairs of the House Intelligence, Oversight and Foreign Affairs committees sent a memo to the White House demanding the key documents they need.

“Over the past several weeks, the committees tried several times to obtain voluntary compliance with our requests for documents, but the White House has refused to engage with — or even respond to — the committees,” they wrote.

Last week, the administration released both a transcript of the phone call, the whistleblower complaint and the inspector general’s report on the matter.

The administration has until Friday to comply with the requests before the committee chairs send out the subpoena.

The summer phone call, during which House Democrats say Mr. Trump pressured the Ukrainian president to investigate Democratic presidential front-runner Joseph R. Biden and his son Hunter, has united Democrats on Capitol Hill and is now at the center of an impeachment inquiry launched by House Speaker Nancy Pelosi last week.

The flurry of subpoenas shows how quickly the Democrats have escalated their impeachment inquiry. So far, the three committees have subpoenaed Secretary of State Mike Pompeo, scheduling depositions for State Department staffers, and Rudolph W. Giuliani, the president’s personal attorney.

Wednesday’s action marks the first time Democrats have threatened to subpoena the White House.

Democrats’ subpoena comes on the same day Steve Linick, the State Department’s inspector general, is scheduled to brief lawmakers about “urgent” material he says is relevant to the Ukraine investigation.

Details on what Mr. Linick intends to reveal remain scant.

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