If you are really interested, I would suggest reading the entire document. There were several proposals made in the Federal Register in June of last year(2007) that proposed round trip cruise ship passengers from a US port be exempt from the final phase of the WHTI regulation. The final document has adopted this with some restrictions. The cruise must depart and return to the same US port and all travel must be within the Western Hemisphere. I find no mention that this excemption will expire at any determined time. The requirement for these cruise passengers is a government issued photo ID and a original or copy of a birth certificate instead of a document designated in this final rule.
This information is on page 29 of the final rule.

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