The US government has launched an appeal against the court ruling which struck down its collection of phone records.
The US government says it is appealing a judge's ruling that the National Security Agency's bulk collection of phone records is unconstitutional and "almost Orwellian."
The Justice Department filed a notice of appeal with the court on Friday following last month's ruling by Judge Richard Leon.
Arguments and briefs in the case will be filed at a later date.
The scathing December 16 ruling by the federal judge in Washington was stayed pending appeal, but if upheld it could lead to the spy agency being barred from indiscriminately monitoring millions of private calls.
"I cannot imagine a more indiscriminate and arbitrary invasion than this systematic and high-tech collection and retention of personal data on virtually every single citizen," Leon said in his opinion.
It is among several court cases pending which challenge the vast surveillance programs spearheaded by NSA and disclosed in documents leaked by fugitive former NSA contractor Edward Snowden.
On December 27, Federal Judge William Pauley in New York dismissed a petition from the American Civil Liberties Union and said the NSA program on phone data was a vital tool to help prevent an Al-Qaeda terror attack on American soil. The ACLU said it would appeal that decision.
The apparently contradictory rulings make it likely the US Supreme Court will decide on the constitutionality of the NSA programs.
Separately Friday, a civil rights group asked the US Supreme Court to review a case challenging the authority of NSA surveillance.
The Centre for Constitutional Rights petitioned the Supreme Court said the Snowden revelations provide new information which should lead the justices to revisit the matter.
"We have always been confident that our communications - including privileged attorney-client phone calls - were being unlawfully monitored by the NSA, but Edward Snowden's revelations of a massive, indiscriminate NSA spying program changes the picture," said CCR lawyer Shayana Kadidal.
"Federal courts have dismissed surveillance cases, including ours, based on criteria established before Snowden's documents proved that such concerns are obviously well-founded."
In a related matter, more than 250 academics from around the world signed an online petition this week calling for an end to "blanket mass surveillance" by intelligence agencies.
The petition said revelations of mass surveillance in documents leaked Snowden violate "a fundamental right" protected by international treaties, including the International Covenant on Civil and Political Rights and the European Convention on Human Rights.
"This has to stop," said the petition (academicsagainstsurveillance.net), an initiative of four academics from the University of Amsterdam.
"Without privacy people cannot freely express their opinions or seek and receive information. Moreover, mass surveillance turns the presumption of innocence into a presumption of guilt... secret and unfettered surveillance practices violate fundamental rights and the rule of law, and undermine democracy.
Signatories included academics from Australia, Hong Kong and New Zealand.