House Intelligence Committee Chair Adam Schiff (D-CA) thinks the vice president’s office may have misled his committee about the contents of his call with the Ukrainian president in September.

In a letter to Vice President Mike Pence on Tuesday said the office’s refusal to declassify records of his call with Ukrainian President Volodymyr Zelensky raises a “serious question” about whether Pence is attempting to hide information from the House’s impeachment efforts. Pence’s office has refused to declassify a portion of his aide Jennifer Williams’ testimony, which she provided as a supplemental submission to the committee in November.

Schiff said the testimony was “directly relevant” to the impeachment inquiry, which is up for a vote on the House floor Wednesday.

“If the Supplemental Submission accurately describes your September 18 conversation with President Zelensky, however, it raises profound questions about your knowledge of the president’s scheme to solicit Ukraine’s interference in the 2020 presidential election,” he wrote to Pence on Tuesday, adding that Pence may be trying to protect himself or the President.

“Contrary to your office’s contention that declassification ‘serves no purpose,’ the additional information in the Supplemental Submission is directly relevant to Congress’s consideration of articles of impeachment against President Trump and the Committee’s ongoing investigation of the President’s Ukraine scheme,” Schiff said. “Furthermore, your unwillingness to declassify the Supplemental Submission raises the serious question of whether your continuing efforts to obstruct the House’s impeachment inquiry are intended not just to protect President Trump, but yourself as well.”

Schiff first asked Pence to declassify the testimony earlier this month.