L-3 Communications, which has sold $39.7 million worth of the machines to the federal government, spent $4.3 million 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. Last year, the company spent $5.5 million on lobbying.

Its lobbyists include Linda Daschle, a prominent Democratic figure in Washington, who is 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 Homeland Security secretary, who has been a prominent proponent of using scanners to foil terrorism. Officials with Chertoff’s firm and Rapiscan say Chertoff was not paid to promote scanner technology. It spent $440,000 on lobbying in 2009.