Federal airport security officials have begun asking travelers to take books and food out of their carry-on luggage, prompting some fliers to complain about a further invasion of the limited privacy they have left at checkpoints.

Transportation Security Administration officials say they are taking the steps on a test basis at a handful of airports nationally mainly because carry-on bags are getting so stuffed that screening agents at x-ray machines are have a hard time seeing what's in the bags.

Some everyday items, including books and magazines, can look similar to explosives when going through the X-ray machine, federal security officials said. Screeners may "fan" through books to see if anything is hidden, TSA official Carrie Harmon said, but Harmon said screeners are not checking to see what people are reading.

University of California, Davis, professor Julie Sze is among those who ran into the new screening procedures Wednesday at Sacramento International Airport. Federal screeners were asking people to take reading materials and food out of their bags and to place those items into a separate bin before sending them along the conveyor belt into the screening machine.

Sze, an American Studies professor at Davis, who was not in the pre-check line, took her cookie out of her bag, but left her magazines in, and went through screening without incident. But, she says, she was annoyed that TSA was pushing privacy boundaries even farther than it already has.

"It's always been a series of insults," she said of security requirements, such as taking off shoes and standing with your hands over your head. "Books, magazines, food, those are like my three treasured things. It feels personal on a whole different level."

Sacramento is not listed as one of the initial "test" airports for the new procedure, TSA officials said, but they noted that the agency "has always incorporated unpredictable screening measures" at airports, including "additional screening at checkpoints."

Los Angeles is one of the test airports, as are Boise, Colorado Springs, Detroit, Fort Lauderdale, Boston Logan, Lubbock, Munoz Marin in Puerto Rico, Las Vegas McCarran, and Phoenix Sky Harbor.

The pilot program currently excludes TSA pre-check lanes, which are reserved for fliers who have submitted applications and received OKs for quicker processing at checkpoints. TSA has a pre-check application office open at Sacramento's Terminal B.

Other travelers nationally are reporting similar experiences over the Memorial Day weekend, the traditional start to the summer flying season when airports see most of their biggest crowds.