A federal lawsuit said the TSA should develop formal regulations for its full-body scanners.

Three groups representing limited government and civil liberties asked the U.S. Circuit Court of Appeals for the District of Columbia to order TSA to propose a regulation governing the use of the machines within 90 days, reported USA Today. 

More than 740 scanners are installed in 160 airports, according to the lawsuit. 

"For four years the TSA has flouted the court's order, preventing the public and outside experts from scrutinizing their actions as required under the law," said Marc Scribner, a CEI research fellow named as a petitioner in the case. "This lawsuit aims to enforce that court decision and bring much needed accountability to an agency plagued by lawlessness."

TSA officials have said full-body scanners are crucial for detecting non-metallic explosives such as the 2009 case of the underwear bomber. Full-body scans are faster than a pat-down, to keep security lines moving, said USA Today.