NEW YORK (AP) — The unprecedented and unwarranted bulk collection of the entire U.S. population’s phone records by the government is illegal because it wasn’t authorized by Congress, a federal appeals court said Thursday as it asked legislators to balance national security and privacy interests.

A three-judge panel of the 2nd U.S. Circuit Court of Appeals in Manhattan permitted the National Security Agency program to continue temporarily as it exists, but it all but pleaded for Congress to better define where boundaries exist or risk “invasions of privacy unimaginable in the past.”

The appeals court said if the government is correct in its legal arguments, it could also justify storing in bulk metadata associated with Americans’ financial records, medical records and electronic communications, including email and social media information.

An opinion written by Circuit Judge Gerald Lynch said Congress could “profoundly alter the legal landscape” after debate.

“Congress cannot reasonably be said to have ratified a program of which many members of Congress – and all members of the public – were not aware,” it said.

“The statutes to which the government points have never been interpreted to authorize anything approaching the breadth of the sweeping surveillance at issue here,” the court said. “The sheer volume of information sought is staggering.”

A lower court judge in December tossed out an American Civil Liberties Union lawsuit, saying the program was a necessary extension to security measures taken after the Sept. 11, 2001, terrorist attacks.

The NSA’s collection and storage of U.S. landline calling records — times, dates and numbers but not content of the calls — was the most controversial program among many disclosed in 2013 by former NSA systems administrator Edward Snowden. Some NSA officials opposed the program, and independent evaluations have found it of limited value as a counterterrorism tool. Snowden remains exiled in Russia.

U.S. Attorney General Loretta Lynch said the government is reviewing the court’s decision. She added that the June 1 expiration of the Patriot Act provisions provides opportunities to reauthorize the program “in a way that does preserve its efficacy and protect privacy.”

The court’s ruling sharpens the focus on the ongoing congressional debate.

Republicans and Democrats in the House have agreed on a bill to end the government’s bulk collection of the records, but Senate leaders are backing a competing measure that would maintain the status quo.

Senate Majority Leader Mitch McConnell and intelligence committee chairman Richard Burr took to the Senate floor Thursday with forceful arguments in favor of continuing the bulk collection. A Senate aide, however, speaking on condition of anonymity because he was not authorized to be quoted about internal deliberations, told The Associated Press the two senators remained open to a compromise that replaces NSA collection with a workable alternative that allows the agency to hunt for terror plots in the U.S.

The divisions on the issue don’t run neatly along partisan lines. Libertarian-leaning Republicans have joined many Democrats in arguing that a secret intelligence agency should not be storing the records of every American phone call, even if the data are only examined under limited circumstances. Some Democrats and Republicans assert that the program is needed now more than ever, given the efforts by the Islamic State group to inspire extremists to attack inside the U.S.

The House Judiciary Committee last month overwhelmingly passed the latest version of a bill known as the USA Freedom Act. The measure seeks to codify President Barack Obama’s proposal to end the NSA’s collection and storage of the phone records. Instead, it would allow the agency to request records held by telephone companies under a court order in terrorism investigations.

Under that proposal, the NSA might end up with access to even more data. As it stands, the program doesn’t collect data on most mobile calls, but under a new arrangement, the NSA could request mobile records as needed from phone companies.

NSA spokesman Edward Price said the agency is evaluating the ruling and added that it’s working closely with Congress on reforms.

Jameel Jaffer, ACLU deputy legal director and lead counsel in the case, said the decision “warrants a reconsideration of all of those programs, and it underscores once again the need for truly systemic reform.”

U.S. Rep. Adam Schiff, D-Calif., a ranking member of the intelligence committee, said he hopes the ruling serves as a “catalyst for an end to bulk collection and the beginning of serious reform.”

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Dilanian reported from Washington. Associated Press writer Eric Tucker in Washington contributed to this report.