"We're demanding President Bush make a commitment to the American people that he will not pardon Scooter Libby, who was involved in this mess, nor will he pardon anyone involved in this mess," Senate Democratic Leader Harry Reid said at a press conference.
"Unless a pardon is ruled out by President Bush, the American people will certainly not learn the truth" about who unmasked CIA agent Valerie Plame, he said.
Senate Democrats restated that demand in a letter to the president Tuesday.
"The indictment of I. Lewis Libby, Vice President Dick Cheneys Chief of Staff, marks the first time in 131 years that a senior White House official has been charged with a crime while still serving in the White House," Democrats wrote.
"Although it is too early to judge Mr Libby guilty or innocent of these particular charges, it is not too early for you to reassure the American people that you understand the enormous gravity of the allegations."
Libby has been charged with perjury and obstruction of justice in the Plame case, and federal prosecutor Patrick Fitzgerald has said additional charges against him and other administration officials could follow.
"We urge you to pledge that if Mr. Libby or anyone else is found guilty of a crime in connection with Patrick Fitzgeralds investigation, you will not exercise your authority to issue a presidential pardon," Democrats wrote in their letter to Bush.
A White House spokesman recently declined to comment on the issue.