Eighteen House Democrats say they want Attorney General Alberto Gonzales to appoint a special counsel to investigate the legality of the Bush administration's eavesdropping program.
The call comes in a letter to President Bush being released Monday.
The lawmakers say the surveillance of terrorists must be done within the bounds of U-S law. They complain that their efforts to get answers to legal and factual questions about the program have been stymied, "generally based on the feeblest of excuses."
The lawmakers initially asked the independent watchdogs at the Justice and Defense departments to open inquiries. Both declined.
Bush administration officials have argued the program does not fall within the Foreign Intelligence Surveillance Act. They also say the power to act came with the authorization for the war on terror.