The US Senate has issued a subpoena ordering the White House to give up documents related to its surveillance of domestic terror suspects.
US citizens' overseas telephone calls were monitored
The Senate Judiciary Committee asked the Bush administration to give up the papers as part of its inquiry into the controversial spying programme.
The administration has refused a series of requests to release the documents.
The president rejects claims that he broke the law by ordering surveillance without first securing warrants.
The programme, authorised after the 9/11 attacks, enabled the government to monitor the overseas e-mail and telephone communications of Americans suspected of ties to terrorists.
While the president says his wartime powers allowed him to authorise surveillance without the need for a warrant, critics say he violated Americans' civil liberties.
The secret spying programme became public in 2005.
The Senate Judiciary Committee's subpoenas target the White House, Vice-President Dick Cheney, the National Security Council and the Department of Justice.
Their intention is to shed light on any discussion that may have taken place within the administration on the legality of the spying programme.
"Our attempts to obtain information through testimony of administration witnesses have been met with a consistent pattern of evasion and misdirection," the Senate Committee's chairman, Patrick Leahy, says.
"There is no legitimate argument for withholding the requested materials from this committee."
The White House has until 18 July to comply with the demand, according to the Democratic-led Senate committee.
It is unclear whether it will do so, or mount a legal challenge to the subpoena.
"We're aware of the committee's action and will respond appropriately," a White House spokesman told the Associated Press news agency.
"It's unfortunate that congressional Democrats continue to choose the route of confrontation."