Washington (CNN) -- A federal appeals court ruled Friday the Transportation Security Administration can still use full-body scanners at airports, but said the agency erred in how it deployed the controversial machines.
A privacy group, the Electronic Privacy Information Center, had sued the TSA claiming the machines violated Fourth Amendment protections against unreasonable searches. The group further argued that the TSA did not follow the required procedures before making significant policy changes, such as subjecting travelers to the full-body scanners.
The three-judge panel of the U.S. Court of Appeals in Washington rejected the first argument, concluding that there was no violation on constitutional grounds. But they agreed on the second point, saying TSA must now go through proper procedures -- though the court, significantly, did not order the agency to stop using the machines immediately.
There is an "obvious need for the TSA to continue its airport security operations without interruption," the judges ruled.
Either side can appeal to the full appeals court or the Supreme Court.
But another, more likely scenario is that TSA, which is part of the Department of Homeland Security, will go through the public comment and rule-making process. The agency's decision following that process could then become the basis for future lawsuits.
"This is not over by any means," said Marc Rotenberg, executive director of the Electronic Privacy Information Center.
TSA officers operate more than 500 of the body imaging machines, which can see through clothes and reveal concealed objects, including bombs and bomb components. TSA plans to have more than 1,000 machines in use at airports nationwide by the end of this year.
Passengers are not required to submit to the scans, and may opt for pat-downs. But, the court noted, "many passengers ... remain unaware of this right, and some who have exercised the right have complained that the resulting pat-down was unnecessarily aggressive."
The Electronic Privacy Information Center argued that the scanners violate passengers' Fourth Amendment rights because, the group claimed, the search is more invasive than necessary to detect weapons or explosives. But the court said the government must weigh "the degree to which (the search) intrudes upon an individual's privacy and... the degree to which it is needed for the promotion of legitimate governmental interests."
"The balance clearly favors the government here," the court said.
Yet the judges took a swipe at the TSA's argument that its plans to implement the technology did not merit a formal public comment and rule-making process.
"It is clear that by producing an image of the unclothed passenger, an (Automated Imaging Technology) scanner intrudes upon his or her personal privacy in a way a magnetometer does not," the court noted.
The court also debunked the privacy group's allegation in its lawsuit that TSA had violated the Video Voyeurism Prevention Act. The judges also labeled as "silly" the claim that the federal agency is not engaged in law enforcement.
The TSA said in a statement that it is reviewing the ruling.
Rotenberg, meanwhile, called the court's decision important and said it "pins" down TSA to a policy in which body scans are optional. Privacy advocates had worried the use of scanners could become mandatory, as they become more ubiquitous at airports.
"I think the court would have had a very different conclusion" had body scans been mandatory, Rotenberg said.