Kevin O’Connor, who served as President Biden’s physician during his term, asked the House Oversight Committee Saturday to postpone scheduled testimony over disagreements on the scope of the questions the Republican-led committee can ask him.

O’Connor is scheduled to give a deposition on Wednesday as part of the committee’s probe into Biden’s mental acuity and his use of an autopen signing device. In a letter to Rep. James Comer (R-Ky.), the chair of the committee, David Schertler, a lawyer for O’Connor, asked to postpone the testimony to the week of July 28 or August 4.

In the letter, Schertler raised concerns that O’Connor would not be able to protect doctor-patient privilege during the testimony, and said that the committee had declined to rule out any limitations to the scope of the deposition.

“Dr. O’Connor has legal and ethical obligations that he must satisfy and for which violations carry serious consequences to him professionally and personally,” the letter reads. “We are unaware of any prior occasion on which a Congressional Committee has subpoenaed a physician to testify about the treatment of an individual patient.  And the notion that a Congressional Committee would do so without any regard whatsoever for the confidentiality of the physician-patient relationship is alarming.”

A spokesperson for the committee told NBC News, which first reported the letter, that O’Connor was attempting to “stonewall” the investigation. The spokesperson said the doctor was welcome to assert that answers to individual questions were private between the doctor and patient during the deposition.

The committee has already interviewed Neera Tanden, the former director of the White House Domestic Policy Council. Top Jill Biden aide Anthony Bernal was previously scheduled to testify but elected not to show, resulting in a subpoena from the committee.