In a sign that the new airport screening procedures may be altered, two key politicians told the Transportation Security Administration today that the rules may be unconstitutional and a waste of government resources.

"We are concerned about the new enhanced pat-down screening protocols and urge you to reconsider the utilization of these protocols," Rep. Bennie Thompson (D-Miss.), the influential chairman of the House Homeland Security Committee, and Sheila Jackson Lee (D-Tex.), chairman of a transportation subcommittee, told the TSA in a letter (PDF). They asked TSA to turn over internal documents, studies, and traveler complaints by December 1.

As the Thanksgiving travel season nears, the reaction to TSA's new procedures has been visceral and sharply critical, driven by cell phone recordings of security line incidents, privacy and health concerns, and Web sites including the Drudge Report, which published a photograph of a hands-on examination of a nun with the caption: "THE TERRORISTS HAVE WON."

Monday's Colbert Report called them machines "that X-ray your X-rated parts," and a software engineer from Oceanside, Calif. became an Internet sensation after telling a TSA screener: "If you touch my junk, I'll have you arrested." (The procedures announced late last month include pat-downs that can touch genitals and full-body scanners that use X-rays.)

The letter demonstrates how some of the agency's political cover is evaporating and could signal a turning point in the protest among Washington politicians. On the other hand, it focuses only on the police-style physical searches, and neither Thompson nor Jackson Lee mentioned the controversial X-ray scanners.

For its part, the TSA shows no visible signs of backing down. It declined to answer questions from CNET this afternoon.

A statement from TSA chief John Pistole said, "All pat-downs are done professionally and are designed to detect hidden explosives that could bring down a plane. Only a small percentage of passengers end up needing them. Pat-downs have long been one of the many security measures TSA and virtually every other nation has used in its risk-based approach to help detect hidden and dangerous items."

Today's letter from the two House Democrats is an abrupt-about face from hearings held just a few days ago, in which Senate Democrats steadfastly backed the Obama administration.

"I think you're doing a terrific job," Jay Rockefeller, a West Virginia Democrat and chairman of the Senate committee overseeing air travel, told Pistole, a former FBI agent who's had the job since July. Sen. Amy Klobuchar, a Minnesota Democrat, said a few minutes later that Americans "have to understand that this is being done for their best interests and their safety."

That echoed what Sen. Joe Lieberman, the chairman of the Homeland Security Committee, said a day earlier. As CNET previously reported, he said the TSA is "doing the right thing," and that the scans and more invasive pat-downs are "necessary for the security--homeland security--of the American people." (Lieberman is an independent senator from Connecticut who caucuses with Democrats.)

Since those pair of hearings, though, the public outcry has continued to grow, with new reports of Americans' encounters with TSA screeners popping up on the Internet, grabbing news headlines, and providing cable TV hosts with a series of anecdotes and poor-quality recordings of security line incidents.

Amateur videos posted on YouTube, including one of a screaming 3-year-old (apparently not even a recent one) being treated none too gently by an airport screener, and bloggers describing how they were "sexually assaulted" after vaginal and labial touching, have put the agency in an unusually difficult position. A Washington Times editorial was titled "Big Sister's police state," and a Forbes writer called for abolishing the TSA outright.

This image of an adult man was taken using a Rapiscan Secure 1000 backscatter X-ray scanner.

One Web site, OptOutDay.com, is recommending what might be called strict civil obedience: it suggests that all air travelers on November 24, the day before Thanksgiving, choose "to opt out of the naked body scanner machines" that amount to "virtual strip searches." Nudeoscope.com, DontScan.us, and StopDigitalStripSearches.org are organizing their own protests.

Thanks to the federal stimulus legislation, TSA has been able to buy nearly 400 whole-body scanners and install them in approximately 70 airports around the country. A few weeks ago, with only a one-paragraph mention on the TSA's Web site, the screening procedures were changed to offer air travelers a choice of either full-body scans or what the TSA delicately calls "enhanced pat-downs."