(CNN) US Ambassador to the European Union Gordon Sondland, a key witness within the State Department and to the President's action in the ongoing impeachment inquiry, intends to testify to the House under subpoena next Thursday, according to his lawyers.

Sondland's testimony will come amid a significant week in the Hill's efforts to hear from witnesses about the Trump administration's dealings with Ukraine, the core of the House impeachment inquiry.

Lawmakers have been eager to press Sondland about text messages he exchanged related to President Donald Trump's July phone call with Ukrainian President Volodymyr Zelensky and the freezing of foreign aid to Ukraine.

As of this morning, Sondland hasn't received guidance from the State Department on whether he should appear under subpoena, his lawyers said in a new statement on his behalf.

"Notwithstanding the State Department's current direction to not testify, Ambassador Sondland will honor the Committees' subpoena, and he looks forward to testifying on Thursday," his attorneys Robert Luskin and Kwame Manley wrote in a statement. "He has no agenda apart from answering the Committees' questions fully and truthfully."

Sondland planned to voluntarily appear on the Hill earlier this week, but his testimony was derailed that morning when the State Department blocked him from testifying. House Democrats issued a subpoena Tuesday evening demanding Sondland turn over documents and appear for a deposition next week.

His attorneys said that despite the subpoena for documents, they aren't able to produce any. That responsibility would fall to the State Department, they said.

"Ambassador Sondland does not control the disposition of his documents," his attorneys' statement said Friday morning. "By federal law and regulation, the State Department has sole authority to produce such documents, and Ambassador Sondland hopes the materials will be shared with the Committees in advance of his Thursday testimony."

Sondland, a Trump donor and hotelier who has been EU ambassador since 2018, exchanged messages with former US special envoy to Ukraine Kurt Volker and a senior US diplomat in Ukraine about setting up the call between Zelensky and Trump and whether foreign aid was being withheld while Trump and his attorney, Rudy Giuliani, pushed for Ukraine to open an investigation into business activity by the son of the President's main Democratic rival, Joe Biden. There is no evidence of wrongdoing by the Bidens.

Three committees in the House plan to hear testimony from four witnesses next week, starting with Fiona Hill, Trump's former top Russia adviser, on Monday, according to a source.

Also on the agenda for next week are Deputy Assistant Secretary George Kent and Counselor Ulrich Brechbuhl, according to the source. While they are scheduled for closed-door interviews, it's possible they will not show up because of the Trump administration's posture to block cooperation.

Sondland may be in a slightly different situation because he was subpoenaed.

The former US ambassador to Ukraine, Marie Yovanovitch, whom Trump spoke negatively about on the call with the Ukrainian President, is scheduled to appear Friday in a closed-door deposition.

This story has been updated.