"A carrier must not board any passenger subject to a "not-cleared" instruction, or any other passenger, or their baggage, unless cleared by CBP."
"The U.S. Department of Homeland Security has proposed a system which will in essence make it mandatory for you to have permission before leaving or entering the country, effectively putting everyone on a no-fly list unless the government says otherwise. Interestingly, the proposal does not seem to cover personal travel, only that on some sort of carrier like an airline or cruise vessel.
In the guise of an NPRM [Notice of Proposed Rule-Making] alleged to propose a change only in the required timing of transmission of information already required to be provided to the Bureau of Customs and Border Protection (CBP), the CBP has actually proposed a fundamental regulatory change with far-reaching (literally and figuratively) legal, policy, and logistical implications: The NPRM would replace a requirement for ex post facto notice to the CBP of information about who is on each vessel (ship or plane) with an unconstitutional system of prior restraint of international travel, entirely unauthorized by statute and inconsistent with the U.S. obligations embodied in the International Covenant on Civil and Political Rights.
Under the proposed rules, orders by the CBP to common carriers not to transport specific persons... would be based on an undefined, secret, administrative permission-to-travel procedure subject to none of the procedural or substantive due process required for orders prohibiting or restricting the exercise of protected First Amendment rights..."