House Democrats leading an impeachment inquiry into President Donald Trump issued subpoenas Thursday to two foreign-born associates of Rudy Giuliani who were charged with campaign finance violations related to a pro-Trump super PAC.

Those businessmen, Lev Parnas and Igor Fruman, were ordered by the leaders of three House committees to provide documents and appear to testify as part of the impeachment probe into Trump.

Giuliani previously said that he had worked with the two men as part of his efforts in Ukraine to push an investigation of former Vice President Joe Biden and his son Hunter, NBC News reported.

John Dowd, an attorney for Parnas and Fruman, did not immediately respond to CNBC's request for comment on the subpoena.

The subpoenas from the Democrats — House Intelligence Chairman Adam Schiff, Oversight Chairman Elijah Cummings and Foreign Affairs Chairman Eliot Engel — were issued less than two days after the White House said it would not cooperate with the impeachment inquiry. The Trump administration blocked a key witness in the probe, U.S. Ambassador Gordon Sondland, from appearing for a deposition earlier this week.

In a letter to Dowd, the chairmen wrote: "Your clients are private citizens who are not employees of the Executive Branch. They may not evade requests from Congress for documents and information necessary to conduct our inquiry. They are required by law to comply with the enclosed subpoenas. They are not exempted from this requirement merely because they happen to work with Mr. Giuliani, and they may not defy congressional subpoenas merely because President Trump has chosen the path of denial, defiance, and obstruction."