A federal appeals court on Friday unanimously declined to block the government from using intrusive body scanners across airports nationwide, saying it is “not persuaded by any of the statutory or constitutional arguments” against them.

The US Court of Appeals for the District of Columbia Circuit was deciding a constitutional and procedural challenge to the Advanced Imaging Technology “nude” body scanners, which began rolling out in 2007 and are deployed to at least 78 airports nationwide. The Electronic Privacy Information Center asked the court to block usage of the devices—of which 500 more are to be rolled out this year—on grounds that they are an unconstitutional privacy invasion, ineffective, and unhealthy to airline passengers.

“The petitioners argue that using AIT for primary screening violates the Fourth Amendment because it is more invasive than is necessary to detect weapons or explosives,” the appeals court noted. “As other circuits have held, and as the Supreme Court has strongly suggested, screening passengers at an airport is an ‘administrative search’ because the primary goal is not to determine whether any passenger has committed a crime but rather to protect the public from a terrorist attack.”

The court said that whether an administrative search is unreasonable is a balancing test on how much it intrudes upon an individual’s privacy, and how much that intrusion is needed for the promotion of “legitimate” government interests.

“That balance clearly favors the government here,” the court ruled 3-0. The court added that an “AIT scanner, unlike a magnetometer, is capable of detecting, and therefore of deterring, attempts to carry aboard explosives in liquid powder form.” The three-judge appellate panel did not address limited research suggesting that the machines might not detect explosives or even guns taped to a person’s body.

However, the appellate court, which is one stop from the Supreme Court, said that the Transportation Security Administration breached federal law in 2009 when it formally adopted the airport scanners as the “primary” method of screening. The judges said the TSA violated the Administrative Procedures Act for failing to have a 90-day public comment period, and ordered the agency to undertake one.

Generally, under the APA, agency decisions must go through what is often termed a “notice and comment” period if their new rules would substantially affect the rights of the public—in this case air passengers. The Environmental Protection Agency often undertakes “notice and comment” periods for proposed pollution regulations.

The court did not penalize the TSA for its shortcomings. The TSA argued to the court in March that a public comment period would thwart the government’s ability to respond to “ever-evolving threats.”

Judge Douglas Ginsburg, writing for the majority, said the TSA must allow for the 90-day notice-and-comment period because of the new “substantive obligations” on airline passengers.

“It is clear that by producing an image of the unclothed passenger, an AIT scanner intrudes upon his or her personal privacy in a way a magnetometer does not. Therefore, regardless whether this is a ‘new substantive burden,’ the change substantively affects the public to a degree sufficient to implicate the policy interests animating notice-and-comment rulemaking," Ginsburg wrote.

“Indeed, few if any regulatory procedures impose directly and significantly upon so many members of the public. Not surprisingly, therefore, much public concern and media coverage have been focused upon issues of privacy, safety, and efficacy, each of which no doubt would have been the subject of many comments had the TSA seen fit to solicit comments upon a proposal to use AIT for primary screening.”

The court declined to address whether the TSA could have skirted the notice-and-comment under a so-called “good cause exception.” That allows agencies to bypass public input when it is “impractical, unnecessary or contrary to the public interest.”

Despite TSA breach, the court would not stop scanner usage. Doing so, Ginsburg wrote, would “severely disrupt an essential security operation.”

Marc Rotenberg, the president of EPIC, the group that brought the challenge, said the decision means the “TSA is now subject to the same rules as other government agencies that help ensure transparency and accountability.”

He said “Many Americans object to the airport body scanner program. Now they will have an opportunity to express their views to the TSA and the agency must take their views into account as a matter of law.”

That said, the court acknowledged “the steps the TSA has already taken to protect passenger privacy, in particular distorting the image created using AIT and deleting it as soon as the passenger has cleared.” During oral arguments in the case in March, Department of Justice lawyer Beth Brinkmann said the government is moving toward adopting new technology that produces a broad outline of a passenger instead of a virtual nude image.

Regarding health concerns, “the agency has commissioned two studies of the safety of the scanners,” Ginsburg wrote. The judge added that the studies—which were not generally accepted in the scientific community—concluded that “the scanners emit levels of radiation well within acceptable limits.”

Ginsburg added that the scanners are optional. “More telling, any passenger may opt-out of AIT screening in favor of a patdown,” he wrote. Ginsburg’s ruling did not address accusations that passengers opting for a patdown are often groped or harassed by TSA security officials.

Joining Ginsburg were Judges Karen Henderson and David Tatel.