A committee has sent a subpoena to the White House demanding documents that could provide details on Donald Trump’s effort to push Ukraine to produce information that could damage Joe Biden’s presidential run.
The subpoena was issued by the House Oversight and Reform Committee as part of Democrats’ impeachment investigation of Mr Trump.
The President has resisted Democratic attempts to produce documents and administration witnesses for the impeachment inquiry.
The subpoena seems likely to escalate the clash between the two branches of government.
Panel chairman Elijah Cummings had threatened the subpoena on Wednesday after the White House ignored two letters in September seeking the documents.
Mr Trump was withholding military aid to Ukraine when he used a July phone call to ask its president to investigate Mr Biden over an unfounded corruption allegation.