"The NSA has trillions of telephone calls and e-mails in their databases that they’ve collected over the last several years,” Greenwald said on ABC's "This Week."
He then detailed the program, which he said only require an e-mail or an IP address to return data on Americans.
Greenwald, who is set to testify on Capitol Hill on Wednesday, suggested intelligence officials are lying when they say low-level staff have no such access to that information. He said he "defies" intelligence officials to deny the program's existence.
“It’s an incredibly powerful and invasive tool -- exactly of the type that Mr. Snowden described,” Greenwald said.
Appearing on the same show, Senate Intelligence Committee Ranking Member Saxby Chambliss (R-Ga.) cast doubt on Greenwald's reporting.
“I was back out at NSA just last week, spent a couple hours out there with high-level and low-level NSA officials, and what I have been assured of is there is no capability ... at NSA, for anyone without a court order to listen to any telephone conversation or to monitor any e-mail," Chambliss said.
Chambliss also said any access that low-level staff had to such personal information would be accidental.
“In fact, we don’t monitor e-mails. That’s what kind of assures me is that the reporting is not correct. Because no emails are monitored now,” Chambliss said. “They used to be, but that stopped two or three years ago. So I feel confident that there may have been some abuse, but if it was it was purely accidental.”