In a letter to Bush on Monday, Conyers said the commutation was troubling and could eliminate Libby's incentive to provide information about the administration's role in leaking the identity of former CIA officer Valerie Plame Wilson.
Libby, who was a top aide to Vice President Dick Cheney, was sentenced to 2 1/2 years in prison for obstructing justice in a federal probe of the leak.
Bush, calling the sentence excessive, used his executive authority last week to commute the sentence, sparing Libby from prison.
Conyers, D-Mich., urged Bush "to waive Executive Privilege and provide the relevant documents and testimony of any relevant aides regarding your decision to commute Mr. Libby's sentence."
The congressman said that his committee on Wednesday will hold a hearing to "explore the grave questions that arise when the Presidential clemency power is used to erase criminal penalties for high-ranking executive branch employees whose offenses relate to their work for the President."
Conyers acknowledged that President Clinton pardoned Marc Rich, whose ex-wife was a major Clinton campaign donor. But Clinton waived executive privilege and allowed top aides to testify before Congress about that matter, Conyers noted in his letter.
The White House did not have an immediate response to the letter.
In another development, White House counsel Fred Fielding told U.S. District Judge Reggie B. Walton that the confusion over Libby's commuted sentence is unnecessary.
Bush forced the CIA leak case into uncharted legal territory last week when he commuted Libby's prison term. The president wiped away the sentence but left in place Libby's two years of supervised release.
But supervised release — a form of probation — is available only to people who have served prison time. Without prison, Walton had said earlier, it's unclear what happens next.
Walton said in court documents that the law "does not appear to contemplate a situation in which a defendant may be placed under supervised release without first completing a term of incarceration."
In a letter to the judge, Fielding said that Libby should simply report to probation officers as if he was recently released from prison. Under supervised release, Libby would have to submit written reports to probation officers each month and secure full-time employment. He would be prohibited from traveling without permission.
Libby has already paid a $250,000 fine.
Special Prosecutor Patrick Fitzgerald and Libby's attorneys were also expected to weigh in on the confusion Monday.