Civil liberties groups are questioning the constitutionality of such warrantless invasions of privacy, but the U.S. Supreme Court has never handed down a nationwide ruling on just what privacy rights an airline passenger has. If and when new measures are challenged, a majority of the justices could decide a passenger gives up the "expectation of privacy" -- the key to invoking constitutional privacy rights -- simply by trying to board an airliner.
The impetus for the new security measures is the alleged Christmas Day attempt by a Nigerian, Umar Farouk Abdulmutallab, 23, to blow up a flight from Amsterdam, Netherlands, over Detroit using explosives hidden in his underwear, out of sight of security screeners. If the attempt had succeeded it would have killed some 300 on the aircraft and an unknown number on the ground.
The attempt allegedly was planned by al-Qaida elements in Yemen, and intelligence reports said there could be more on the way.
Under ferocious public pressure, the Obama administration conducted a review of intelligence failures and the Transportation Security Administration prepared to set up electronic full-body scanners for many passengers attempting to enter the United States. The scanning would even apply to U.S. citizens returning home from designated, usually Muslim, countries.
"Because effective aviation security must begin beyond our borders, and as a result of extraordinary cooperation from our global aviation partners, TSA is mandating that every individual flying into the U.S. from anywhere in the world who holds a passport issued by or is traveling from or through nations that are state sponsors of terrorism or other countries of interest" -- a total of 14 countries -- "will be required to go through enhanced screening," the TSA said in a statement Jan. 3. "The directive also increases the use of enhanced screening technologies and mandates threat-based and random screening for passengers on U.S. bound international flights."
In addition, the agency is implementing unspecified measures at U.S. airports. The TSA said: "At this time, security checkpoint requirements for passengers departing U.S. airports remain the same. Passengers do not need to do anything differently, but they may notice additional security measures at the airport."
Other parts of the statement seemed to point to Muslims and others wearing ethnic clothing.
"TSA's current procedures for the screening of bulky clothing or head wear remain unchanged," the agency said. "To ensure the highest level of security, passengers wearing loose fitting or bulky clothing -- including head wear -- may be subject to additional screening. In instances where passengers choose not to remove bulky clothing, including head wear, our officers are trained to offer a private screening area and may conduct a pat down search to clear the individual."
In the Netherlands, officials say in the wake of the Christmas Day attempted bombing, all passengers headed for the United States will undergo full-body scans, and British officials pledge to use full-body scanners as well.
In the United States, 40 scanners are used at 19 airports, including Reagan National and Baltimore-Washington International, the Atlanta Journal-Constitution reported. But only six are used for the primary security search. The TSA has ordered 150 more scanners and has funding for an additional 300.
Groups such as the American Civil Liberties Union point out the screened images of passengers are essentially naked, with genitals exposed, to determine whether explosives are being carried under a passenger's clothes.
Faces would be blurred, and U.S. security officials insist the images cannot be transmitted to the Internet.
But Isaac Yeffet, former head of El-Al airlines, told Fox News Muslims would not tolerate widespread use of the devices.
"Realize that a Muslim will know that his wife was seen naked in this machine," he said. "You know what would be the reaction? ... Terrible."
The ACLU responded to the new security measures by saying: "The government should adhere to longstanding standards of individualized suspicion and enact security measures that are the least threatening to civil liberties and are proven to be effective. Racial profiling and untargeted body scanning do not meet those criteria."
Michael German, national security policy counsel at the ACLU Washington Legislative Office and a former FBI agent, said in a statement, "Overbroad policies such as racial profiling and invasive body scanning for all travelers not only violate our rights and values, they also waste valuable resources and divert attention from real threats. ... "
"Singling out travelers from a few specified countries for enhanced screening is essentially a pretext for racial profiling, which is ineffective, unconstitutional and violates American values," he added. "Empirical studies of terrorists show there is no terrorist profile, and using a profile that doesn't reflect this reality will only divert resources by having government agents target innocent people. Profiling can also be counterproductive by undermining community support for government counter-terrorism efforts and creating an injustice that terrorists can exploit to justify further acts of terrorism."
The ACLU said a British study indicated the full-body scanners would not be effective, and "according to security experts, the explosive device used in the attempted attack on a Detroit-bound plane on Christmas Day would not have been detected by the body scanners."
Also from Washington, the American-Arab Anti-Discrimination Committee said it "is deeply concerned by the new Transportation Security Administration ... directives ... (that) will require citizens from 14 countries, all Arab or Muslim countries, with the exception of Cuba, to go through enhanced security screening. Such screening can include full pat-downs, scans, delays and anything associated with secondary screening -- an extra search of the passenger's carry-on luggage may also be required. News sources also stated that the directives are applicable to any travelers, including U.S. citizens, who have passed through one of these 14 countries, or who have taken flights that have originated from these 14 countries."
In the absence, at least for now, of an overarching U.S. Supreme Court decision, how would U.S. courts react to all this deep concern, assuming a legal challenge is initiated against taking pictures of one's naughty bits while trying to fly to the United States?
At least two U.S. circuit courts of appeal have beaten back challenges to airport security measures.
In 2006, the 3rd U.S. Circuit Court of Appeals -- Justice Samuel Alito's old stomping grounds -- ruled a suspicionless, unwarranted search during airport screening was allowable under the "administrative search doctrine."
The doctrine, an exception to searches requiring court warrants, was developed by the courts over a number of years. In a 1971 ruling, the 9th U.S. Circuit Court of Appeals said the doctrine meant "searches conducted as part of a general regulatory scheme in furtherance of an administrative purpose, rather than as part of a criminal investigation to secure evidence of a crime, may be permissible under the Fourth Amendment though not supported by a showing of probable cause directed to a particular place or person to be searched."
In other words, if the main objective of the search is to prevent an act of terror instead of finding evidence to prosecute a suspect, then the doctrine applies. Over the years the doctrine has been used to justify metal detectors at airports, government buildings and schools.
In 2007, the 9th Circuit -- considered the most liberal appeals court in the country -- ruled U.S. airline passengers could be searched at any point after checking in, and could no longer avoid a search by leaving the airport, which sometimes had been the case in the past.
As for the Supreme Court, the justices refused to review a 9th Circuit ruling in 2007 that said passengers could not board an airliner without showing a government-issued ID.
But a high court refusal to review a case or an issue does not set a precedent. What the Supreme Court does have is a standard explaining when people should have an expectation of privacy, a necessary element of the Fourth Amendment's ban on "unreasonable" searches and seizures.
Justice John Marshall Harlan wrote the standard in a 1967 case, which he said he had gleaned from court precedent. Harlan's standard came in an separate concurring opinion agreeing with the majority in a wiretap case, but the Supreme Court has since adopted it for all cases.
Harlan said there was a twofold Fourth Amendment requirement, first that someone has "exhibited an actual (subjective) expectation of privacy and, second, that the expectation be one that society is prepared to recognize as 'reasonable.'"
Are objections to full-body scans by people who have done nothing to give authorities a reason to suspect them "reasonable?" Or is the government's use of the scans to prevent acts of terror even more "reasonable?"
The U.S. courts, and eventually the Supreme Court, may have to provide the answer.
2014: The Year in Music [PHOTOS]