A federal judge on Monday issued a temporary restraining order blocking the White House from destroying back-up copies of deleted e-mails.
The order by US District Judge Henry Kennedy came in a lawsuit by the Citizens for Responsibility and Ethics in Washington, a private watchdog group, which claims the White House has failed to preserve millions of deleted e-mails it was supposed to keep.
The group, CREW, filed suit against the Executive Office of the President and the National Archives and Records Administration in September.
CREW said it sought a temporary restraining order after the White House refused to give adequate assurances that it would preserve backup copies of the deleted e-mails.
The White House said it would study the court's order, but said it has been taking steps to maintain and preserve backup tapes for its e-mail system.
"We have provided assurances to the plaintiffs and to the court that these steps were being taken. We will continue preserving the tapes in compliance with the court's order," White House spokesman Blair Jones said in an e-mail.
The White House has said it was aware that some e-mails may not have been automatically archived, but may be available on backup tapes. It has given no estimate of the number of messages that might not have been archived.
"Today's order is an important and necessary first step toward restoring and preserving for the public all the records of this administration, not just those self-elected for preservation," CREW said in a statement.
CREW and the National Security Archive, an independent research institute at The George Washington University, filed separate lawsuits challenging whether the White House has violated federal and presidential record keeping laws.