The National Security Agency, the country's primary surveillance agency, told CNN in a statement: "One of the biggest misconceptions about NSA is that we are unlawfully listening in on, or reading e-mails of, U.S. citizens. This is simply not the case. NSA is unwavering in its respect for U.S. laws and Americans' civil liberties."
Sen. Ron Wyden, D-Oregon, proposed an amendment requiring more disclosure.
"I think we ought to know, generally, how many Americans are being swept up under the legislation," he said during Thursday's debate on the Senate floor.
But defenders of the law say, the effectiveness of espionage programs depends on a level of secrecy.
"It's very hard to have covert and clandestine intelligence-gathering, if it's not secret," said Clifford May, an advocate of national security with the Foundation for Defense of Democracies.
Without reauthorization, the law was scheduled to expire Monday, at the end of 2012.