House Democrats on Thursday subpoenaed Department of Energy Secretary Rick Perry for Ukraine documents as part of their impeachment investigation against President Donald Trump.

“Recently, public reports have raised questions about any role you may have played in conveying or reinforcing the President’s stark message to the Ukrainian President,” the letter reads from the chairmen of the House Intelligence, Oversight, and Foreign Affairs committees.

BREAKING: Intelligence, Oversight and Foreign Affairs Committees subpoena Energy Secretary Rick Perry for documents related to his potential involvement in conveying or reinforcing Trump's efforts to press Ukraine for dirt on a political opponent.https://t.co/xHuO8Zova3 — House Intelligence Committee (@HouseIntel) October 10, 2019

The lawmakers requested that Perry turn over the documents by October 18th.

The development comes after Perry’s spokesperson confirmed the Energy Secretary encouraged President Trump to discuss energy and economic issues with the leader of Ukraine during their July 25th telephone call, which was mischaracterized by a partisan CIA officer in a so-called “whistleblower” complaint. The officer’s complaint has since sparked House Democrats to launch an impeachment inquiry.

“Secretary Perry absolutely supported and encouraged the president to speak to the new president of Ukraine to discuss matters related to their energy security and economic development,” Shaylyn Hynes, a Perry spokesperson, said in a statement.

President Trump on Friday evening told House Republicans that it was Perry who had teed up the July call with Ukraine, according to a person familiar with Trump’s new comments who was granted anonymity to discuss the private conference call.

But President Trump did not suggest that Perry had anything to do with the pressure on Ukraine to investigate the Bidens, or a U.S. holdup in military aid to the country, the person said. The president’s remarks on the late Friday call was first reported by Axios.

Perry, the former governor of Texas and up to now a lower-profile but active member of Trump’s Cabinet, has made repeated trips to Ukraine and met often with Ukranian officials, including Zelenskiy. Perry and his agency say his involvement with Ukraine was part of U.S. policy, predating the Trump administration, to increase U.S. natural gas, coal and other supplies to Eastern Europe to lessen Russia’s control of the region’s energy market.

“He continues to believe that there is significant need for improved regional energy security,” Hynes said. Perry was heading to Lithuania again Sunday night, and would meet with nearly two dozen European energy officials, including those from Ukraine, she said.

Both President Trump and Zelensky have denied any pressure was applied to probe Biden, whose alleged corruption in Ukraine and China has garnered negative attention for the former vice president amid sinking 2020 poll numbers and a rising candidacy of rival Sen. Elizabeth Warren (D-MA).

“There was no blackmail,” Zelensky told reporters when asked Thursday about his call with President Trump. “We are not servants. We are an independent country.”

“I don’t want to be pulled into this because I understand that my words could impact the elections of the American people,” he added.

The Associated Press contributed to this report.