President Trump’s personal attorney Rudy Giuliani was subpoenaed for documents Monday by Democrats on the House Intelligence Committee, as the impeachment inquiry into the president accelerates.

The Democratic chairmen of the House committees on foreign affairs, intelligence and oversight gave Giuliani a deadline of Oct. 15 to turn over documents he referenced in TV interviews regarding his conversations with Ukrainian officials. The documents include “text messages, phone records and other communications” that could indicate which other administration officials were involved.

“Your failure of refusal to comply with the subpoena, including at the direction of behest of president or the White House, shall constitute evidence of obstruction of the House’s impeachment inquiry and may be used as an adverse inference against you and the president,” the letter says.

They also requested depositions with three of Giuliani’s business associates: Lev Parnas, Igor Fruman and Sam Kislin.

This letter follows another subpoena for documents from Secretary of State Michael Pompeo, as the Democratic-led House committees try to sustain the momentum of the impeachment inquiry sparked last week by a whistle-blower report. The report detailed Trump’s conversation to pressure Ukranian President Volodymyr Zelenskiy to investigate former Vice President Joe Biden, now a leading 2020 rival to Trump.

Trump recommended that Zelenskiy reach out to Giuliani for guidance on allegations regarding Biden and his son, Hunter.

Giuliani, 75, a former mayor of New York City and Trump’s personal lawyer, has continued to advance claims that Biden as vice president used leverage to force out Ukraine’s top prosecutor in order to protect his son who served on the board of Ukrainian energy company Burisma Holding from prosecution. Biden has said he forced out the prosecutor in order to foster more anti-corruption probes, and Ukrainian officials have said Hunter Biden was not under investigation.

On Sunday, Giuliani said on ABC News’ “This Week” he would refuse to cooperate with House Intelligence Committee Chairman Adam Schiff, whom Trump has accused of treason.