Senate Democrats said that Tuesday's discovery of some unreleased documents from Supreme Court nominee John Roberts (search) could make things tougher for him at his confirmation hearings next week.

"If these documents reveal significant information about Judge Roberts' views and we are not getting them until the eve of the hearings, there could well be a need for additional time to question the nominee," said Sen. Charles Schumer, D-N.Y., a member of the Judiciary Committee.

The National Archives announced on Tuesday that the Ronald Reagan Presidential Library (search) in Simi Valley, Calif., had discovered a "large volume" of unreviewed and unreleased Roberts documents that were filed under a code instead of under Roberts' name. Additional employees from the Archives have been sent to the Reagan library to review the documents to determine what or how much can be released, officials said.

Roberts' confirmation hearing will begin next Tuesday.

The National Archives has said some of the documents could be "duplicative" of those already released, said Sen. John Cornyn, R-Texas.

"Tens of thousands of documents have already been released -- more than any Supreme Court nominee in history," Cornyn said. "And with each new release of information, it's growing increasingly difficult for the president's opponents to complain with a straight face about the need for more information."

Democrats noted that at least one file of Roberts documents on affirmative action has gone missing, and the White House is refusing to let them see Roberts' documents from his time in the solicitor general's office during the George H.W. Bush administration.

"The Judiciary Committee has been hard at work preparing for expedited hearings on this important nomination, and there is no doubt that this last-minute revelation is a hindrance to that preparation," said Sen. Patrick Leahy, D-Vt., the senior Democrat on the committee.