A rule, not a law voted on, but now proposed by the Dept of Homeland Seccurity on "Passenger Manifests for Commercial Aircraft Arriving in and Departing From the United States; Passenger and Crew Manifests for Commercial Vessels Departing From the United States" will make travel restrictions a reality if it passes. Check out  USCBP-2005-0003 at the government's own website, after clicking on "Advanced search", then "docket search":

http://www.regulations.gov/fdmspublic/component/main

   These new rules are said to take effect January 14, 2007, but the travel industry is saying it will take a year to implement.

   The Notice of Proposed Rulemaking, NPRM, would create a clearly invalid administrative presumption, reversing the presumptions of innocence and of entitlement to the exercise of First Amendment rights, that all those persons not affirmatively “cleared” in advance by the Bureau of Customs and Border Protection, CBP,  according to decision-making procedures and criteria specified nowhere in the NPRM – are barred from travel.

   The proposed rules would burden equally, and infringe the rights to varying degrees of U.S. citizens, resident aliens, immigrants, nonimmigrant visitors, and even those with no intention to enter the U.S. who merely wish to travel on flights that will, or might, transit through U.S. airspace. Reciprocal adoption of similar rules by other countries would further burden travel worldwide by U.S. citizens and residents, including their international travel and their travel within the USA.

   Under the rules proposed by this NPRM, “A carrier must not board any passenger subject to a ‘not-cleared’ instruction, or any other passenger, or their baggage, unless cleared by CBP.” This rule would authorize prior restraint on, and presumptive denial of, the Constitutional right to travel. The proposed rules would prohibit air and sea common carriers from transporting any person without the express prior permission of the CBP, creating a regime of prior restraint and presumptive denial of the right to travel and to assemble.

    Following is the response from Homeland Security to the questions asked about travel restrictions:

   Commenters to the previous APIS NPRM, 68 Fed. Reg. 292 (January 3, 2003), expressed concerns on some of these issues to which the DHS issued this response:

   Several commenters remarked that collection of information through APIS would infringe on the right to travel as recognized by the Supreme Court in Kent v. Dulles, 357 U.S. 116 (1958).

   Response: CBP recognizes, as the Supreme Court has stated, that the right to travel is an important and long-cherished liberty. Although a passenger's refusal to supply the information required by the regulatory text will result in denying that person access to international travel on commercial vessels and aircraft, the new provisions will not violate a constitutional right to travel. The Supreme Court has recognized that the right to travel abroad is not an absolute right, and the Court has recognized that no government interest is more compelling than the security of the nation. Haig v. Agee, 453 U.S. 280, 307 (1981). The government may place reasonable restrictions on the right to travel in order to protect this compelling interest. Id.; see also Eunique v. Powell, 302 F. 3d 971, 974 (9th Cir. 2002); Hutchins v. District of Columbia, 188 F. 3d 531, 537

(D.C. Cir. 1999).