The California Democrat said the CIA had hacked into computers used by the committee to conduct a long-running review of Bush-era treatment of terrorism suspects.
Feinstein said CIA Director John Brennan told her in January the agency searched the computers because it believed the committee investigators had gained access to a classified internal CIA review they were not authorized to see.
"The CIA did not ask the committee or its staff if the committee had access to the internal review or how we obtained it," Feinstein said in a scathing speech on the Senate floor Tuesday. "Instead, the CIA just went and searched the committee's computer."
Feinstein says her team, sorting through millions of documents related to years of terrorism-related interrogations and investigations, used only a search tool provided by the CIA to sort through the material.
”I have grave concerns that the CIA’s search may well have violated the separation of powers principles embodied in the United States Constitution,” she said. “It may have undermined the constitutional framework essential to effective Congressional oversight of intelligence activities."
Brennan, speaking later Tuesday morning, flatly denied Feinstein's accusations.
"As far as the allegations of CIA hacking into Senate computers -- nothing could be further from the truth," Brennan told the Council on Foreign Relations. "We wouldn't do that. I mean that's, that's, that's just beyond the scope of reason."
Both sides had been grumbling about the other stepping outside the law. The Justice Department is getting involved and considering whether to launch an investigation into the committee's review, which involved millions of documents kept at a Virginia facility specifically for that purpose.
Notable deaths of 2014 [PHOTOS]