Three congressional committees have subpoenaed Secretary of State Mike Pompeo for documents related to efforts by President Donald Trump and his personal lawyer, Rudy Giuliani, to dig up dirt on 2020 presidential candidate Joe Biden.

The House Foreign Affairs, Intelligence, and Oversight committees threatened the subpoenas earlier this week, giving the department until Friday to turn over documents to Congress.

“The subpoenaed documents shall be part of the impeachment inquiry and shared among the Committees,” according to a letter sent by the committees to Pompeo Friday. “Your failure or refusal to comply with the subpoena shall constitute evidence of obstruction of the House’s impeachment inquiry.”

Pompeo has emerged as a key figure in the Ukraine saga after Giuliani roped in the Secretary of State during a Fox News appearance on Wednesday, when he said he had never spoken to anyone in Ukraine “until the State Department called me and asked me to do it.” Pompeo, an especially close ally of the president, has stayed mum this week on what exactly his role has been.

Officials from the State Department, according to the anonymous whistleblower who first raised the issue to lawmakers, wound up serving as mediators, reportedly explaining to the the Ukrainian government how to “navigate” Trump’s requests to see Biden and his son, Hunter, investigated.

House Democrats opened up another front of their Ukraine inquiry on Friday: figuring out whether or not $400 million of U.S. security aid to Ukraine was delayed due to Trump’s interest in the Biden investigation. The House Appropriations and Budget Committees requested a tranche of documents from the Office of Management and Budget in hopes of establishing how and why that aid—granted to Ukraine without incident since 2015—stalled over the course of the last several months before being released earlier in September. The whistleblower’s complaint only glances at the issue of the held-up aid, which is at the heart of whether Trump attempted to establish a quid-pro-quo with Ukrainian President Volodymyr Zelensky.

It’s unclear if the committees will also subpoena witnesses of Trump’s communications with Ukrainian officials or if they will call on Giuliani for questioning. Asked Monday if he would cooperate and agree to an interview on Capitol Hill, the Trump attorney said, “No, not [with] the corrupt ones like Schiff and Nadler.” Giuliani also cited attorney-client privilege between him and the president.

Friday’s salvo represents the first serious move by House Democrats to learn more about the substance of an explosive complaint from an anonymous whistleblower, which has become the basis of their newly-minted impeachment inquiry.

The whistleblower complaint, made public on Thursday, laid out efforts by Trump, Giuliani, and other U.S. officials to pressure Ukrainian officials—including the president, Volodomyr Zelensky—into investigating the business dealings of Biden’s son, Hunter, in the country. It also documents the unusual steps White House officials took to conceal not only a conversation between Trump and Zelensky but other conversations between the president and different foreign leaders, too.

In addition to the subpoenas, the committees also teed up depositions, scheduled to take place over the next two weeks, of five State Department officials key to the Ukraine probe. They include Gordon Sondland and Kurt Volker—the U.S. ambassador to the European Union and the U.S. special envoy for Ukraine, respectively—whom the whistleblower alleges were tasked with helping Ukrainian officials navigate Trump’s expectations.

The first person scheduled to be deposed is Marie Yovanovitch, the former U.S. ambassador to Ukraine who was recalled in May under circumstances the whistleblower described as politically motivated. Trump called Yovanovitch “bad news” in his July call with Zelensky.

Members of the House Intelligence Committee—which is taking a lead role in the Ukraine-focused impeachment probe—will remain in Washington for at least a portion of the upcoming two-week recess to continue building evidence.

In a Friday letter to colleagues, Intelligence Committee Chairman Adam Schiff (D-CA) said the chairs “ will be actively working on these matters throughout the recess.” He also revealed that the committee will hold a closed briefing with the Inspector General of the Intelligence Community—the official who first explained to lawmakers why the whistleblower’s complaint was being held up by administration officials—on October 4.

“More subpoenas and investigatory steps will occur next week, as the investigation accelerates,” Schiff continued, “and we will update you as those steps become public.

The Daily Beast first reported in June that Democrats on Capitol Hill were preparing to open an investigation into Giuliani’s work in Ukraine as it related to Biden and whether it worked against U.S. foreign policy interests. That investigation has expanded since then to include Trump’s communications with Zelensky as well as the State Department’s overtures to Giuliani and other Ukrainian officials.

The investigating congressional committees requested documents related to their probe from Pompeo more than two weeks ago.