Some travelers at key airports in New York and Los Angeles may be put through machines that see through clothing and provide a detailed image of a person's body beginning later this week.

It's the first expansion of the program since the machines were first put to the test in Phoenix, Arizona.

The "whole body imaging" machines have sparked complaints from privacy advocates.

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But the Transportation Security Administration says that it has taken steps to protect individuals' privacy and that 90 percent of the travelers in Phoenix preferred the imaging machine to a pat-down.

The millimeter wave machines will be rolled out at John F. Kennedy International Airport in New York and Los Angeles International Airport in California later this week, TSA Administrator Kip Hawley told Congress on Tuesday.

The TSA will be purchasing at least 30 more machines for use at other U.S. airports this year, he added.

The TSA will use two different methods at JFK and LAX as they study the most effective way to use the machines.

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