We’re in the throes of a busy holiday travel season, yet most travelers are probably unaware of new regulations involving airport body scanners.

The Department of Homeland Security published new rules Dec. 18 limiting the ability of travelers to decline a body scan at airport checkpoints operated by the Transportation Security Administration (TSA).

Before then, travelers who thought the X-ray-like scanning technology was too revealing could request a body pat-down. Now, if the TSA deems you a “security consideration,” it can require you to go through the scanner, even if you request the physical search.

Airports began deploying the scanners — known as Advanced Imaging Technologies (AIT) — in 2007, including Minneapolis-St. Paul International Airport. They’re the walk-in booths where you raise your hands and stand still for about 15 seconds. The scanner screens passengers for prohibited items, such as hidden weapons and explosives, without physical contact.

The scanners have provoked legal challenges claiming they’re nothing more than strip searches that violate basic human rights. Early images essentially showed the nude body of the person being scanned, but TSA has since upgraded its technology to reveal objects against the background of a generic human figure.

TSA officers screen some 660 million passengers a year at 440 airports nationwide using about 750 body scanners.

It’s unclear whether recent terror incidents, such as the shootings in San Bernardino, Calif., prompted the new rule. TSA isn’t saying much publicly.

In a statement, TSA said most passengers will still have the option to decline body scanning in favor of a pat-down. “However, some passengers will be required to undergo [body scanner] screening if warranted by security considerations in order to safeguard transportation security. This will occur in a very limited number of circumstances where enhanced screening is required. The vast majority of passengers will not be affected.”