Former White House aide Harriet Miers will continue to refuse to appear before a House committee, her lawyer said Tuesday despite Democrats' threats to hold her in contempt.

"Ms. Miers will not appear before the committee or otherwise produce documents or provide testimony," lawyer George T. Manning said in a letter to the committee.

The House Judiciary Committee had given Miers, President Bush's former legal counsel who defied a subpoena to appear before the committee, until Tuesday to change her mind about testifying. Lawmakers have been investigating whether the White House was involved in the dismissals of eight federal prosecutors.

"Her failure to comply with our subpoena is a serious affront to this committee and our constitutional system of checks and balances," House Judiciary Chairman John Conyers, D-Mich., said. "We are carefully planning our next steps."

Any contempt proceedings would first be considered by the committee and later by the full House. If a majority of the House approves a contempt order, Speaker Nancy Pelosi, D-Calif., would refer the matter to the U.S. attorney for the District of Columbia, Jeff Taylor, a Bush appointee.

While Democrats say Miers made her own decision not to appear, Manning said in the letter that Bush told her to defy the committee because of executive privilege. Democrats say her immunity ended when she left her White House job.

The White House is also claiming executive privilege on e-mails on the firings sent by White House officials on Republican National Committee-sponsored accounts. Those documents also have been subpoenaed with a Tuesday return date, but Conyers agreed to give the RNC until July 31 to turn over the documents or explain why not.

A Judiciary subcommittee will meet on Thursday to consider the White House's executive privilege claim.

Bush and Attorney General Alberto Gonzales have denied wrongdoing in the dismissal of the federal prosecutors, maintaining they are political appointees who can be fired by the president for almost any reason.

Conyers on Tuesday also asked for Justice Department documents involving its prosecution of former Alabama Gov. Don Siegelman, Wisconsin state procurement official Georgia Thompson and Cyril Wecht, a Pennsylvania coroner.

Democrats have alleged that all three prosecutions were politically motivated. The Justice Department has insisted there was no political involvement.

On another front, the Senate Judiciary Committee on Tuesday agreed to give the White House more time to respond to its subpoena for documents relating to Bush's controversial eavesdropping program that operated warrant-free for five years.

The committee wants documents that might shed light on internal disputes within the administration over the legality of the program, which Bush put under court review earlier this year.

"However, it has become clear that we will not be able to come close to completing our review process by the July 18 return date," Fred Fielding, the White House counsel, wrote in a letter to the committee.

Senate Judiciary Chairman Patrick Leahy, D-Vt., said he would work with the administration.