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GPO’s explanations have not satisfied lawmakers, who are poised to dig deeper.

Mr. Dingell, the House Commerce chairman, said The Times’ findings are “extremely serious to both the integrity of the e-passport program and to U.S. national security” and he has asked an investigative subcommittee chaired by Rep. Bart Stupak, Michigan Democrat, to begin an investigation.

“Our initial inquiry suggests that more needs to be done to understand whether the supply chain is secure and fully capable of protecting the manufacturing of this critical document,” Mr. Dingell told The Times.

Mr. Stupak said that considering the personal information contained on e-passports, “it is essential that the entire production chain be secure and free from potential tampering.” He added: “The GPO needs to make every effort to ensure that future passport components are made in America under the tightest security possible.”

Michelle Van Cleave, a former National Counterintelligence Executive, said outsourcing passport work and components creates new security vulnerabilities, not just for passports.

“Protecting the acquisition stream is a serious concern in many sensitive areas of government activity, but the process for assessing the risk to national security is at best loose and in some cases missing altogether,” she told The Times.

“A U.S. passport has the full faith and credit of the U.S. government behind the citizenship and identity of the bearer,” she said.

“What foreign intelligence service or international terrorist group wouldn’t like to be able to masquerade as U.S. citizens? It would be a profound liability for U.S. intelligence and law enforcement if we lost confidence in the integrity of our passports.”