Show us your papers.
In the U.S., there are numerous possible starting points for a national identification system, with the Social Security Administration, the 'National Highway Traffic Safety Administration' and the 'Department of Health and Human Services' being the top candidates. Since most Americans have a Social Security or a driver's license number, it has become increasingly common for everyday transactions to require the use of these numbers as proof of identity.
It's very likely that any national ID proposals that make it through will be labelled "voluntary". That is, if you never plan to get a job, vote, travel, cash a check, open a bank account, go to the hospital, enrol in a public school, receive Medicare or other federal benefits, purchase insurance, then it is voluntary. Otherwise you must comply. Got it?