On Tuesday, three judges at one of the nation’s most powerful appellate courts will hear oral arguments in the only legal challenge to result in a judicial order against the National Security Agency’s (NSA) vast telephone metadata collection program. That order was put on hold pending the government’s appeal in this case.

The District of Columbia Circuit Court of Appeals could overturn last year’s unusual lower court ruling that ordered an end to the program, or the court could confirm it.

The lawsuit, known as Klayman et al v. Obama et al, pits a longstanding conservative lawyer, Larry Klayman, against the American government and its intelligence apparatus. If Klayman wins, the suit is likely to be eventually appealed further to the Supreme Court.

Klayman filed his federal lawsuit at the District of Columbia District Court on June 6, 2013, the day after the first disclosures from the Snowden leaks were published. The very first story revealed that Verizon had been routinely handing over all metadata on its customers to the NSA. And as a Verizon customer, Klayman argued that his constitutional rights were violated as the result of such data handover, not to mention the rights of all other Verizon customers.

The government relied primarily, as it has done numerous times in similar cases, on a 1979 Supreme Court decision known as Smith v. Maryland. That case famously established the "third-party doctrine," holding that information (such as call metadata) disclosed to a third party (like Verizon) cannot be private as it was by definition shared with that third party. Therefore, the argument goes, it can be disclosed to the government without any violation of privacy.

But Judge Richard Leon, a Republican appointee, agreed with Klayman’s argument. He wrote in a December 16, 2013 memorandum opinion:

Indeed, the question in this case can more properly be styled as follows: when do present-day circumstances—the evolutions in the Government's surveillance capabilities, citizens' phone habits, and the relationship between the NSA and telecom companies—become so thoroughly unlike those considered by the Supreme Court 34 years ago that a precedent like Smith simply does not apply? The answer, unfortunately for the government, is now. … In sum, the Smith pen register and the ongoing NSA Bulk Telephony Metadata Program have so many significant distinctions between them that I cannot possibly navigate these uncharted Fourth Amendment waters using as my North Star a case that predates the rise of cell phones.

Judge Leon ordered the government to immediately halt the Bulk Telephony Metadata Program and to destroy "any such metadata in its possession that was collected through the bulk collection program." But, he noted, "in light of the significant national security interests at stake in this case and the novelty of the constitutional issues, I will stay my order pending appeal."

That appellate process reaches a significant stage on Tuesday, with oral arguments from not only Klayman, but from other amici speaking on his behalf from the ACLU, the Electronic Frontier Foundation (EFF), and the Center for National Security Studies (a DC-area think tank).

Jesselyn Radack, one of Snowden’s lawyers, told Ars by e-mail that the judge’s language was eyebrow-raising.

"Judge Leon’s decision that the precedent isn’t controlling is unusual, but not unprecedented, though it is the kind of decision usually made at the appellate court level," she said. "That Judge Leon was willing to break with the court’s standard operating procedure in this way speaks to how strongly he believes Klayman’s rights were violated."

An "unusually intrusive program"

Civil libertarians and privacy activists are closely watching the case to see if the appellate court upholds the landmark lower court order. Since Klayman originally filed his lawsuit, there have been a few notable policy and legal decisions that could push the appeals court in his favor.

Specifically, the Supreme Court has taken a stronger view of digital privacy than it has in the past. Earlier this year, in a unanimous decision in the Riley v. California case, the nine justices found that law enforcement must get a warrant before they search someone’s cellphone.

On the policy side, both the Congressionally mandated Privacy and Civil Liberties Oversight Board (PCLOB) and the president’s Review Group on Intelligence and Communications Technologies (RGICT) recommended that the metadata collection program should end as they currently exist.

PCLOB, in particular, concluded in January 2014 that the government’s metadata collection program "lacks a viable legal foundation under Section 215 [of the Patriot Act], implicates constitutional concerns under the First and Fourth Amendments, raises serious threats to privacy and civil liberties as a policy matter, and has shown only limited value… As a result, the board recommends that the government end the program."

The RGICT recommended that the NSA not be allowed to hold all that metadata in-house. Either way, both conclusions are simply advisory—they are not binding law by any means. The metadata program still functions in essentially the same way that it did before the American public heard of Edward Snowden.

"Over the last year, the government’s privacy boards have taken the view that this unusually intrusive program is unnecessary," Patrick Toomey, an attorney with the American Civil Liberties Union (ACLU), told Ars. "I’m hopeful that [the appellate court] will find that this is unconstitutional. Judge Leon was persuaded that bulk surveillance is a way of collecting information that raised a significant violation of a reasonable expectation of privacy and the Constitution."

Will conservative judges be swayed?

Legal experts are divided as to whether Judge Leon’s appellate counterparts, who are all also Republican appointees, will be willing to challenge the government’s view.

"The three judges who will be hearing the Klayman appeal on the DC Circuit skew conservative," Ruthann Robson, a constitutional law professor at the City University of New York, told Ars. "Interestingly, Judge Sentelle and Judge Brown, who are both on Klayman's panel, were also on the panel that voted in favor of the constitutionality of the Military Commissions Act, which was later declared unconstitutional by the United States Supreme Court in Boumediene v. Bush. But one judge, Judge David Sentelle, who is known as a national security expert, joined the DC Circuit's opinion, another judge, Judge Janice Rogers Brown, a conservative with a decided libertarian bent, dissented. The third judge on Klayman's panel is the 78-year-old Stephen Williams, appointed by Ronald Reagan."

Brian Owsley, himself a former federal district judge in Texas and now a law professor at Indiana Tech, told Ars that he didn’t think that partisan politics was a good predictor of outcomes. "There are people on both the right and the left who are finding common ground in voicing a myriad of privacy concerns."

However, Radack, Snowden’s lawyer, thinks Klayman will face an uphill battle.

"Judges Brown and Sentelle are the more conservative justices on the panel and are very likely to defer to agency authority in this case as they have in the past (Sentelle wrote an opinion in 2010 arguing that the right of habeas corpus does not extend to those detained at Bagram airbase)," she said by e-mail. "Though Judge Williams is the least conservative and more sophisticated on these issues, he is also likely to defer to the NSA."

Radack added that the two recent unanimous Supreme Court decisions in favor of privacy—the Riley case and the 2012 case, United States v. Jones, which found that police cannot warrantlessly install a GPS tracker on a car—"bolster Judge Leon’s argument that the 1979 Smith v. Maryland case should no longer be controlling precedent on questions about the legality of government surveillance."