Liberal activists responded strongly to the Guardian report. Former Vice President Al Gore called "blanket surveillance obscenely outrageous" and the American Civil Liberties Union called the practice "alarming."
"It is beyond Orwellian, and it provides further evidence of the extent to which basic democratic rights are being surrendered in secret to the demands of unaccountable intelligence agencies," ACLU deputy legal director Jameel Jaffer said.
A large grassroots group -- the Progressive Change Campaign Committee -- also launched an "emergency petition" demanding an immediate congressional investigation of the Obama administration.
Attorney General Eric Holder, who was already scheduled to appear before a Congressional committee today, declined to go "into anything specific" with the lawmakers, but told them members of Congress have been "fully briefed" on the issue. Holder agreed to testify before another committee in a classified setting about the program.
White House spokesperson Josh Earnest told reporters travelling on Air Force One that the president welcomes the debate over the NSA program.
"The president welcomes the discussion of the trade-off," Earnest said, referring to the tension between national security and personal liberty.
ABC News' Lee Ferran, Sunlen Miller, Abby Phillips and Z. Byron Wolf contributed to this report.