Judges who issued the harshest rebuke to the National Security Agency have expressed skepticism at a civil libertarian attempt to stop the twilight phase of US bulk phone records surveillance, one of two challenges to the NSA in federal courtrooms.

Alex Abdo of the American Civil Liberties Union argued on Wednesday before a three-judge panel of a federal appeals court in New York that the NSA should not be allowed to collect Americans' phone data in bulk during a "transition" period seemingly allowed under a new law that bans the controversial surveillance. 

The transitionary period for the bulk NSA collection under the new USA Freedom Act still relies on the same statutory authority as before, Abdo noted – the provision of the 2001 Patriot Act that the same judges on the second circuit court of appeals in Manhattan said in May did not in fact bless the NSA program. 

"The harm we're suffering has no expiration date," Abdo argued, contending that the continued surveillance, which expires on 28 November under the new surveillance regime Congress passed in June, has a chilling effect on the civil liberties group's work.