The refusal of an American air traveller to go through a body scanner has given rise to an internet sensation, and has the U.S. government defending the controversial machines.

John Tyner posted an internet blog item about his refusal to undergo a full-body scan or pat-down at San Diego International Airport. (Rebekah Butler/Associated Press)California software engineer John Tyner, 31, recorded himself challenging security agents at San Diego International Airport during the weekend.

When he was singled out for a body scan, Tyner refused, as he was entitled to do provided he instead submitted to a body pat-down by an agent.

The security agent explained to Tyner that he would have to touch his groin area.

"We can do that out here, but if you touch my junk I'm going to have you arrested," Tyner is heard saying on the recording.

Tyner offered to go through a metal detector, but eventually was escorted back to the ticketing area, where he obtained a refund.

When he went to leave the airport, another official stopped him and said he would face a fine of $10,000 US and a lawsuit if he didn't go back to security screening. Tyner refused, and left the terminal.

He documented his experience on the internet, where video of his airport encounter has been viewed hundreds of thousands of times, and he has done a series of media interviews.

Tyner's refusal has led to online sales of T-shirts, bumper stickers, hats and underwear with the words, "Don't Touch My Junk!"

At least one person has launched an online campaign urging airline passengers to refuse all body scans on Nov. 24, the heavy travelling day before U.S. Thanksgiving. Brian Sodergren, 33, of Virginia, created the "National Opt-Out Day" website a week ago, and interest has taken off since Tyner's story emerged.

"The outpouring has been huge," said Sodergren, who is suggesting travellers refuse only a body scan, not a pat-down.

"The proper reaction isn't walking away and subjecting yourself to penalties," he said. "The proper response is to write to your lawmakers and get the law changed."

Homeland Security Secretary Janet Napolitano has responded by defending pat-downs and the increasing use of body scanners.

"We're not doing this just to do it," she said. "We're doing it because we need to keep powders and gels and liquid off of planes that are unauthorized, just as we need to keep metals off of planes."

The head of the U.S. Transportation Security Administration told politicians in Washington, D.C., that travellers who refuse a body scan and a pat-down, even if they cite religious reasons, won't be allowed to fly.

"That person is not going to get on an airplane," John Pistole said during an appearance before the Senate homeland security committee.

With files from The Associated Press