While some officials, such as former U.S. special representative for Ukraine relations Kurt Volker, testified voluntarily last week, there is a growing number of subpoenas being issued for individuals and government bodies to assist the inquiry.

Here’s who has been subpoenaed in the impeachment inquiry so far. 

Secretary of State Mike Pompeo

At the end of last month, three House committees subpoenaed Secretary of State Mike Pompeo for documents related to the Ukraine probe. In their letter to Pompeo, the heads of the House Foreign Affairs, Oversight, and Intelligence committees noted that they had requested the documents on two earlier occasions, to which Pompeo failed to comply. They further noted that Pompeo’s actions are “troubling,” as it has become clear that “multiple State Department officials have direct knowledge of the subject matters of the House’s impeachment inquiry.”

The deadline to comply with the subpoena was Friday, Sep. 4. As of Sunday, Pompeo had yet to come into compliance. 

The White House

Last Friday, the House Oversight Committee issued a subpoena to the White House, which was sent to Acting Chief of Staff Mick Mulvaney. The subpoena requested all documents related to Ukraine, including the July 25 call between Trump and Ukrainian President Volodymyr Zelensky, the temporary halting of aid to Ukraine, and any pressure to investigate former Vice President Joe Biden and his son Hunter.

On Tuesday, the White House sent a letter to Pelosi and the chairs of the three House committees saying that it would not cooperate. Calling the inquiry “invalid,” and the requests “baseless, unconstitutional efforts to overturn the democratic process,” it argues that Trump has “no choice.” “In order to fulfill his duties to the American people, the Constitution, the Executive Branch, and all future occupants of the Office of the Presidency,” the letter reads. “President Trump and his Administration cannot participate in your partisan and unconstitutional inquiry under these circumstances.” 

The letter is signed by White House Counsel Pat Cipollone. The White House reportedly plans to block any other witnesses from testifying and documents from being provided.

Pelosi responded in a statement Tuesday, saying that “continued efforts to hide the truth of the President’s abuse of power from the American people will be regarded as further evidence of obstruction.”

Rudy Giuliani

The House committees subpoenaed Trump’s personal lawyer Rudy Giuliani late last month for documents related to Ukraine. Giuliani has until October 15 to comply, but appears unlikely to do so, after criticizing the subpoena. Giuliani called the committee a “joke” in an interview, arguing that it’s “the McCarthy committee on steroids. There’s no sensitivity to civil rights.”

Department of Defense and Office of Management and Budget

On Monday, Oct. 7, the House subpoenaed the Department of Defense (DOD) and Office of Management and Budget. The DOD subpoena involves a request for documents encompassing all of the matters in the aforementioned subpoena to Pompeo. The OMB subpoena, meanwhile, is tied to its involvement in the freezing of foreign aid to Ukraine.

The two agencies have not yet responded, but The Wall Street Journal has reported that a DOD spokesman said that they “are prepared to work with Congress and other relevant parties on questions related to the issue of Ukrainian aid as appropriate.”

U.S. Ambassador to the EU Gordon Sondland

The House committees subpoenaed U.S. Ambassador to the EU Gordon Sondland on Tuesday evening, after the State Department instructed him not to testify before Congress. Sondland also reportedly has text messages or emails relevant to the investigation that he had shared with the State Department, which has refused to share these with the House.

The subpoena demands that Sondland share the documents by October 14, and appear for a deposition on October 16. The House had already made a voluntary deposition request.

Vice President Mike Pence

Thus far, the House committees have only sent a letter to Vice President Mike Pence requesting documents related to the inquiry. He has not been subpoenaed, but if he doesn’t meet the October 15 deadline, that may change.

House Democrats have also scheduled a number of depositions, including for former U.S. ambassador to Ukraine Marie Yovanovitch, who is due to appear on Friday, as well as Deputy Assistant Secretary George Kent, and State Department Counselor T. Ulrich Brechbuhl.

They may issue subpoenas for three others, Lev Parnas, Igor Fruman, and Sem­yon Kislin, who reportedly helped Giuliani in Ukraine and have refused to comply with summonses from Congress.

While House Democrats have suggested that any efforts to block the investigation may constitute impeachable acts of obstruction, Congress has limited ability to actually enforce the subpoenas they’ve issued.