Large-scale surveillance, on top of the Obama administration's crackdown on national security leaks, threatens the freedom of the press and the right to legal counsel, Human Rights Watch and the American Civil Liberties Union said in a joint report.
The National Security Agency's surveillance programs, which include the collection of telephone "metadata," have heightened government officials' concerns about dealing with the media, as "any interaction - any email, any phone call - risks leaving a digital trace that could subsequently be used against them," the report said.
The groups interviewed more than 90 journalists, lawyers, and current or former senior U.S. government officials for the report.
"Journalists told us that officials are substantially less willing to be in contact with the press, even with regard to unclassified matters or personal opinions, than they were even a few years ago," the report said.
The Obama administration has been more aggressive than recent predecessors about silencing leakers, and has charged eight people under the Espionage Act on suspicion of leaking information. In the wake of disclosures by former NSA contractor Edward Snowden, the administration has stepped up efforts to detect "insider threats" from government employees who might want to leak information.
Many current U.S. surveillance programs go well beyond what is necessary to ensure national security, the report said.
"The U.S. holds itself out as a model of freedom and democracy, but its own surveillance programs are threatening the values it claims to represent," report author Alex Sinha said in a statement.
The report called on President Barack Obama and Congress to reform U.S. surveillance policies, as well as reduce secrecy and provide greater protection for whistleblowers.
The U.S. House of Representatives passed a bill in May to end the NSA's bulk collection of telephone data. It is now under consideration in the Senate.
Department of Justice spokesman Marc Raimondi said in an email that the DOJ "supports the First Amendment rights of all Americans and we are continuously balancing the need to protect national security with respect for the freedom of the press."
Raimondi criticized the report's methodology.
"This report relies more on opinions and less on facts or statistics to bolster its claims," he said.
© Thomson Reuters 2014