The National Security Agency disclosed in a classified Capitol Hill briefing this week that it does not need a court order to listen to domestic phone calls, according to CNET.
CNET said the authorization appears to extend to e-mail and text messages too because the same legal standards apply to Internet communications.
Earlier this week, the top Democrat on the House Judiciary Committee accused the Obama administration of breaking the law by collecting the phone records of millions of Americans.
"It seems clear the government's activity exceeds the authority this Congress has provided — both in letter and in spirit," Rep. John Conyers (D-Mich.) said during a Judiciary Committee oversight hearing of the FBI.
The Guardian newspaper published a secret court order last week that required Verizon to turn over the phone records of millions of its customers to the FBI and the NSA. The records include phone numbers, call time, call duration and other information, but not the contents of the conversations themselves.
The secret court order was based on Section 215 of the Patriot Act, which allows the government to collect business records but requires that they must be "relevant" to a terrorism investigation.
CNET said its latest report was unrelated to disclosure that the NSA is collecting metadata related to Verizon calls, but appears to confirm some of the allegations made by Edward Snowden, the former NSA employee who leaked documents to the Guardian.
The warrantless surveillance of domestic phone calls raises serious "constitutional problems," Kurt Opsahl, a senior staff attorney at the Electronic Frontier Foundation, told CNET.
The NSA declined to comment on CNET's latest report.
--Brendan Sasso contributed to this report.