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.

“My bag was searched by TSA because I was carrying too many books,” one wrote.

“Well, that was the first time that TSA asked me to take my books out of my carry-on along with my laptop,” another wrote.

The TSA sent The Bee an official statement that said the agency has in the past year been “adjusting screening procedures at select U.S. airports on a trial basis in an effort to improve screener performance at the checkpoint … Travelers at select test locations may be asked to place certain electronics and other items in a separate bin for screening in an effort to de-clutter baggage. TSA will evaluate the results at these test locations to determine if any future checkpoint procedures should be altered.”

The Wall Street Journal reported last week that TSA officials said screeners will be more engaged with passengers at the front tables where people put items into bins to pass through the x-ray machines. The official told the Journal that screeners will ask people to remove more items, including electronics, from their bags, but those items may differ from line to line and airport to airport.

Officials told the Journal that some items, such as chocolate and books, are dense and can obscure other items when passing through the x-ray.

Tony Bizjak: 916-321-1059, @TonyBizjak