The federal government has not sufficiently improved the process for people barred from flying over the U.S. to challenge their placement on the no-fly list, lawyers for six people on the list told a federal judge Wednesday.

Attorneys from the American Civil Liberties union said the government is not providing enough information for people labeled as potential terrorists to clear their names.

"This is a day and age in which the 'terrorism threat' label is a very, very serious one. It is perhaps the most stigmatizing one that the government can place on people," ACLU lawyer Hina Shamsi told the judge. "And our clients are still asking for a reasonable process to recover their constitutionally protected interests."

The no-fly list decides who is barred from flying at U.S. airports. It contains thousands of names and has been one of the government's most well-known counterterrorism tools since 9/11. It also has been one of the most criticized, with opponents saying some innocent travelers have been mistaken for terrorism suspects.

U.S. District Judge Anna Brown of Portland, Oregon ruled last year that the government offers no adequate method for people to contest the travel ban, depriving them of constitutional rights.

In response, federal authorities created an appeals process. They also began acknowledging that people were on the list and, when possible, providing unclassified information justifying their placement.

"The government has taken extraordinary steps, we believe, to accommodate the plaintiffs' interests," U.S. Department of Justice attorney Brigham Bowen told the judge.

Lawyers for the government say the rules comply with last year's court order and are necessary to protect national security. The government has long maintained that the list requires secrecy to shield sensitive investigations, protect informants and to avoid giving terrorists clues for avoiding detection.

The ACLU says the new rules don't give people enough information to offer a reasonable defense. The group says people deprived of their right to travel must have a chance to see the evidence against them, challenge accusers and offer a defense in an adversarial hearing.

The case was originally filed in 2010 by 13 people denied the right to fly. After last year's court ruling, the government notified seven of them that they were free to fly.