L-3 Communications, which has sold $39.7 million worth of the machines to the federal government, spent $4.3 million trying to influence Congress and federal agencies during the first nine months of this year, up from $2.1 million in 2005, lobbying data compiled by the Center for Responsive Politics show. Its lobbyists include Linda Daschle, a former Federal Aviation Administration official.

Rapiscan Systems, meanwhile, has spent $271,500 on lobbying so far this year, compared with $80,000 five years earlier. It has faced criticism for hiring Michael Chertoff, the former Homeland Security secretary, last year. Chertoff has been a prominent proponent of using scanners to foil terrorism. The government has spent $41.2 million with Rapiscan.

"The revolving door provides corporations like these with a short cut to lawmakers" and other decision-makers, said Sheila Krumholz, of the Center for Responsive Politics.