The ABA group, which includes a one-time FBI director and former federal appeals court judge, said the president has overstepped his authority in attaching challenges to hundreds of new laws.

The attachments, known as bill-signing statements, say Bush reserves a right to revise, interpret or disregard measures on national security and constitutional grounds.

"This report raises serious concerns crucial to the survival of our democracy," said the ABA's president, Michael Greco. "If left unchecked, the president's practice does grave harm to the separation of powers doctrine, and the system of checks and balances that have sustained our democracy for more than two centuries."