The US Government’s practice of collecting millions of Americans' phone records has been ruled illegal.

A federal appeals court has found that the National Security Agency’s digital surveillance regime - revealed by former government security contractor Edward Snowden – is not authorised by the Government’s anti-terrorist Patriot Act.

The ruling has put pressure on the US Congress to decide whether to replace or end the controversial surveillance dragnet.

Circuit Judge Gerard Lynch - part of a three-judge panel – made the ruling on Patriot Act Section 215, which covers the FBI's ability to gather business records.

The judges found that it was inappropriate to interpret the section to permit the NSA to collect a “staggering” amount of phone records, contrary to claims by the Bush and Obama administrations.

“Such expansive development of government repositories of formerly private records would be an unprecedented contraction of the privacy expectations of all Americans,” Lynch wrote in a 97-page decision.

“We would expect such a momentous decision to be preceded by substantial debate, and expressed in unmistakable language. There is no evidence of such a debate.”

The court did not rule on whether such mass surveillance violated the U.S. Constitution, and did not call for a halt to the intrusive practice, leaving it up to Congress to continue the debate.

Parts of the Patriot Act, including Section 215, will expire on June 1.

US Attorney General Loretta Lynch told at a Senate budget hearing following the decision that NSA data collection was a “vital tool in our national security arsenal”, and that she had not heard of privacy violations under the program.

If Congress does keep the NSA program alive, courts may be asked to review the nature of what it does.

Experts say that if Congress allows Section 215 to remain as it is, further litigation before the Supreme Court is likely.

The White House's National Security Council says the Barack Obama regime hopes to end the NSA program, calling the recent ruling
“good progress” on the path to find an alternative that preserves the “essential capabilities” of the spy department.

Just days before the new finding, the House Judiciary Committee voted 25-2 to cease the bulk collection of telephone data through the USA Freedom Act.

This bill is to be presented for a vote by the full House, where it is expected to pass, while the White House has signalled support for it too.

Key figures of the Senate, Majority Leader Mitch McConnell and Intelligence Committee chair Richard Burr, both Republicans, want to extend Section 215 and other parts of the Patriot Act to run at least to 2020.

The NSA program has been approved in secret numerous time by a national security court based on a 1978 law - the Foreign Intelligence Surveillance Act.

“FISA has been critically important in keeping us safe in America,” McConnell said.

Senators from all sides took to Twitter to welcome last week’s decision.

Senator Rand Paul, a Kentucky Republican, said
“phone records of law abiding citizens are none of the NSA's business!”

Senator Bernie Sanders, a Vermont Democrat, tweeted “the NSA is out of control and operating in an unconstitutional manner”.

The latest ruling came just over a week after US District Judge Richard Leon said the “almost Orwellian” program could violate Fourth Amendment limitations on warrantless searches.

Leon issued an injunction to block the program, which has been put on hold pending appeals.

The Electronic Frontiers Foundation has published an in-depth analysis of the findings, and what they could mean for the future of the scheme and for the personal right of US citizens.