A recent investigation into the National Security Agency's electronic eavesdropping activities has found that the federal agency exceeded its authority to wiretap Americans, the New York Times reported this week.

The revelations, made by numerous unnamed sources in the story, come nine months after the agency gained the right to wiretap terrorism suspects without a warrant. Last July, Congress passed, and President Bush signed, the Foreign Intelligence Surveillance Act (FISA) Amendments Act of 2008, giving the U.S. government greater leeway in wiretapping foreign terror and espionage suspects and granting legal immunity to telecommunications companies that cooperated with the Bush Administration in the past.

In classified briefings, the NSA has said that implementing its new surveillance powers has led to a number of cases where the wiretaps exceeded their authorization, according to the New York Times. Officials and lawyers familiar with the matter said the surveillance was "significant and systemic, although one official said it was believed to have been unintentional," the paper stated.

"When inadvertent mistakes are made, we take it very seriously and work immediately to correct them," the Office of the Director of National Intelligence told the newspaper.

The National Security Agency has been at the center of a number of debates over the monitoring of individuals' information. In 2005, the NSA became the focus of the wiretapping debate when the Timesreported that the agency had eavesdropped on the Internet activities and phone calls of U.S. citizens as well as foreign terrorism targets without seeking the warrant required by law. More recently, the agency has pressed its case to lead the United States' efforts in cyberspace.

The American Civil Liberties Union (ACLU) argued that the latest news supports its call for a review of the new surveillance powers granted to the NSA.

"It’s time to fulfill that promise and restore the checks and balances of our surveillance system," Caroline Fredrickson, director of the ACLU's Washington Legislative Office, said in a statement. "Warrantless surveillance has no place in an America we can be proud of. These revelations make it clear that Congress must now make a commitment to rein in government surveillance."

The U.S. Department of Justice acknowledged to the New York Times that there may have been problems, but stated that they had been resolved.