The National Security Agency may be allowed to continue scooping up American phone records indefinitely even if congressional authority for the spying program expires later this year, according to a recently declassified court order.

The legal underpinning of the NSA's bulk collection of U.S. call data resides in a provision of the post-9/11 USA Patriot Act that is scheduled to sunset on June 1. The common understanding among lawmakers and the intelligence community is that the surveillance program will halt unless Congress reauthorizes Section 215 of the Patriot Act in some fashion.

But a passage buried on the last pages of an order from the Foreign Intelligence Surveillance Court declassified last week leaves open the door for the program—exposed publicly by Edward Snowden nearly two years ago—to continue even if lawmakers let Section 215 lapse.

"If Congress, conversely, has not enacted legislation amending [Section 215] or extending its sunset date," writes Judge James Boasberg, "the government is directed to provide a legal memorandum … addressing the power of the Court to grant such authority beyond June 1, 2015."

The possibility of the NSA program continuing absent congressional reauthorization was raised last year by The New York Times, which pointed to an obscure provision of the Patriot Act that allows the government to continue indefinitely a foreign intelligence investigation that is ongoing and that began before the bill's expiration.

The Times article noted that administration officials were dubious that President Obama would support leaning on such circular justification to continue the NSA's mass collection of phone metadata—the time stamps, numbers, and locations of a call, but not its actual contents—or that the surveillance court would accept the rationale.

But Boasberg's order, which renewed the phone-records program until June 1 and was highlighted by civil-liberties advocate and journalist Marcy Wheeler, appears to be the first time such a scenario has been openly considered by the government.

"It's certainly a concern," said Liza Goitein, codirector of the Liberty and National Security Program at the Brennan Center for Justice, which just released a report urging a bevy of FISA Court reforms. "There's no way that the federal government is going to respond to this by submitting a legal memorandum that says it does not have the authority to do any more spying."

The NSA did not respond to a request for comment on whether its bulk collection could continue without congressional reauthorization. Robert Litt, general counsel for the Office of the Director of National Intelligence, said during a call with reporters last month that the Obama administration had no contingency plan for continuing the spying program if Congress failed to act. But he added, "We'll figure out what we're going to do."

Many privacy advocates believe the White House would have two routes available if it chose to continue the program, absent congressional action. Along with potentially being able to continue investigations that are ongoing despite an expiration, the administration could also rely on a "pen/trap" statute, which allows for phone tapping and has a loose standard of relevancy, akin to Section 215, and typically does not require probable cause.

Stewart Baker, a former general counsel at the NSA, said it's possible the surveillance court could use the leeway to grant a "one-off measure" in May to keep the bulk-records program going only through June. He noted that Boasberg's order requests that a memorandum from the government be filed not by June 1 but by May 22, a notable deadline, given that "most observers expect that Congress will only act at the last minute."

"The much harder question is whether it could issue any orders in June," Baker said. "There's an argument that it can, but I suspect that the administration won't be willing to make that argument."

But while Obama has called for NSA reforms and urged a transition that would effectively end bulk collection, future administrations may possess the capacity to unilaterally reactivate that surveillance, said Harley Geiger, policy counsel at the Center for Democracy & Technology.

"Even if this administration did not seek to continue existing bulk-collection programs after a sunset, a future administration may be able to do so," Geiger said. "The legal argument for continuing the programs is tied to the investigations—and the government's terrorism investigations have no time limit."

Others were more skeptical that Obama wouldn't simply let the program expire and wait for Congress to pass reform legislation.

"What would be the point of the sunset if the government could do the same things the day after the sunset that it could do the day before?" said Jameel Jaffer, deputy legal director of the American Civil Liberties Union. "The government usually takes a broad view of its surveillance authority, but this interpretation of the law is such a stretch that I will be surprised if even the government adopts it."

Obama has not openly shown a desire to pull additional strings to keep the program running—which would likely bring political repercussions within his own party, to say nothing of Republicans who already believe he has overstepped his executive authority in other areas. The president has repeatedly called on Congress to send him a bill to his liking that curtails the NSA's surveillance apparatus.

Still, privacy advocates said they have been endlessly surprised by the government's interpretation of laws related to national security and intelligence-gathering.

"This would not be the first time that the NSA and the FISA Court stretched the meaning of the law beyond what seems reasonable," Goitein said. "It is a weak argument, but it is no weaker than arguments that this administration has put forward and that this FISA court has blessed."

It remains unclear how much political will there is in Congress to tackle NSA reform, amid a spate of national security concerns, such as the rise of ISIS. The USA Freedom Act, a bill that would have curtailed several aspects of the NSA's spying regime, died in the Senate last November. The measure fell two votes shy of the 60-vote threshold necessary to advance, despite backing from the administration and senior intelligence officials.

All but four Republicans voted down the Freedom Act, because then-Minority Leader Mitch McConnell and others warned it could undermine spies' ability to thwart terrorism. Sen. Rand Paul, a vocal critic of government surveillance and likely GOP presidential contender, opposed the bill, saying he would rather let the Patriot Act expire than reform the existing authorities.