Once this is implemented it will become a passport that you have to show when crossing state lines. It will be used to track your movements within the country.
Washington Post Editorial Board:
The case for a national ID card
An effective solution would be to issue tamper-proof, biometric ID cards — using fingerprints or a comparably unique identifier — to all citizens and legal residents. Last week, both President Obama and a bipartisan group of eight senators seeking immigration reform urged something along those lines, without calling it a universal national identity card. That’s a major step forward.
Critics on both the civil-liberties left and the libertarian right have long resisted such cards as the embodiment of a Big Brother brand of government, omniscient, invasive and tentacular. Their criticisms ring hollow.
More than a third of Americans (35 percent) possess passports, up from just 6 percent 20 years ago — and all passports issued since 2007 contain chips that enable biometric use of facial recognition technology. The proliferation of passports for foreign travel has not encroached on Americans’ civil liberties. Why would another form of ID, used for employment verification, pose such a threat?”