Sen. Bernie Sanders, I-Vt., wrote Friday to the head of the National Security Agency demanding to know if the agency secretly gathered intelligence on members of Congress.

"Has the NSA spied, or is the NSA currently spying, on members of Congress or other American elected officials?" Sanders asked in his short letter to Gen. Keith Alexander, the NSA director.

Sanders said "spying" would include gathering metadata on phone calls made from official or personal phones, content from websites visited or emails sent, or collecting any other data from a third party not made available to the general public.

The outspoken Sanders added he was "deeply concerned" by revelations that American intelligence agencies harvested the phone records, emails and web activity of millions of innocent Americans without reason to suspect them of illegal activity.

Sanders said "equally disturbing" reports that the United States eavesdropped on the leaders of Germany, Mexico, Brazil and other allies have "caused serious foreign policy setbacks for the United States, weakened our ability to work cooperatively with our allies and caused an increase in anti-American sentiment throughout the world."

Sanders, along with other members of Congress, have proposed legislation that would curb the NSA’s authority.

The federal government must be "vigilant and aggressive" in protecting the country against terrorism, Sanders said. "I believe, however, that we can do that effectively without undermining the constitutional rights that make us a free country," he said.