The Senate began debating a new immigration reform measure recently, and it has privacy hounds up in arms. The legislation involves creating a national database of biometric information on every adult in the United States.

What exactly do they mean by "biometric information"? Well, in this case, it may not be as insidious as it sounds. Part of the Border Security, Economic Opportunity, and Immigration Modernization Act, the 800-page document (.pdf) is intended to address unlawful employment of undocumented immigrants. The section on the proposed "photo tool" describes a massive federal database that is administered by the Department of Homeland Security and stores names, ages, Social Security numbers and photographs of everybody in the country, along with a driver's license or official photo ID.

To be fair, in its current state, this measure does not extend to some dystopian initiative to chronicle every characteristic and activity of every person in the country. But it's clear that the critics are fearful this could lead to that. The ACLU has said it believes this could be a first step to keeping records on all residents and their activities in some sweeping national identification system.

The idea is for employers to use the database for hiring purposes, but the ACLU explains that such limitations are rarely maintained. The group cites the Social Security card as an example. The intention of these numbers was to track government retirement benefits, but they're now required for things like procuring health insurance, loans, credit and much more.

Taken to an extreme, the government could feasibly wind up using the database to track everyday activity. Here's a scenario: At first, it's used for employment. Then it's mandated for identity purposes, like registering at polling places or opening a checking account. Before you know it, people are checking you in at sporting events and concerts or requiring photo verification before letting you log into the Internet. And all that data is being warehoused by Homeland Security.

This is what the privacy groups are concerned about. Wired put it well: "Think of it as a government version of Foursquare, with Big Brother cataloging every check-in."

The measure hasn't passed yet, as the debate is ongoing. The session will pick up again this Tuesday.