Is there a reference under U.S. law for the recent VWP passport requirement changes?
Yes. The USA-PATRIOT Act legislated that each Visa Waiver Program traveler must have a machine-readable passport. The Department of Homeland Security (DHS), Customs and Border Protection (CBP) began full enforcement of this policy on June 26, 2005. Additionally, the 2002 Enhanced Border Security and Visa Entry Reform Act created a requirement that VWP travelers present machine-readable passports (MRP) which are tamper-resistant and incorporate biometric identifiers in compliance with guidelines established by the International Civil Aviation Organization.