US Vice President Dick Cheney has declined to turn over documents sought by Congress in an inquiry into how the Bush administration's energy policy was formed, according to letters from Mr Cheney.
Mr Cheney said in letters to the House of Representatives and the Senate that the request for meeting records of President Bush's energy task force, which was headed by the vice president, "would unconstitutionally interfere with the functioning of the executive branch."
An aide to California Democratic US Rep. Henry Waxman, one of the lawmakers who originally requested the information, said Mr Cheney appeared to be heading for a legal showdown.
"It looks like they are sort of intent on going to court," said the aide, speaking on condition of anonymity.
A senior Cheney aide said Mr Cheney's office had already provided "substantial information" and that the task force had acted properly.
Mr Cheney's office said the letters were delivered to Congress Thursday night, ahead of an August 7 deadline for a response and the same day as the US House of Representatives approved legislation embodying major elements of the energy plan that task force developed.
"Preservation of the ability of the executive branch to function effectively requires respecting the confidentiality of communications among a president, the vice president, the president's senior advisors and others," Mr Cheney's letter said in an attached appendix.
It said the GAO lacked authority to investigate the performance of the president or vice president in carrying out their constitutional duties.